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Sample records for laser photorefractive keratectomy

  1. Laser-assisted subepithelial keratectomy (LASEK) versus photorefractive keratectomy (PRK) for correction of myopia

    PubMed Central

    Li, Shi-Ming; Zhan, Siyan; Li, Si-Yuan; Peng, Xiao-Xia; Hu, Jing; Law, Hua Andrew; Wang, Ning-Li

    2016-01-01

    Background Myopia (near-sightedness or short-sightedness) is a condition in which the refractive power of the eye is greater than required. The most frequent complaint of people with myopia is blurred distance vision, which can be eliminated by conventional optical aids such as spectacles or contact lenses, or by refractive surgery procedures such as photorefractive keratectomy (PRK) and laser epithelial keratomileusis (LASEK). PRK uses laser to remove the corneal stroma. Similar to PRK, LASEK first creates an epithelial flap and then replaces it after ablating the corneal stroma. The relative benefits and harms of LASEK and PRK, as shown in different trials, warrant a systematic review. Objectives The objective of this review is to compare LASEK versus PRK for correction of myopia by evaluating their efficacy and safety in terms of postoperative uncorrected visual acuity, residual refractive error, and associated complications. Search methods We searched CENTRAL (which contains the Cochrane Eyes and Vision group Trials Register) (2015 Issue 12), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to December 2015), EMBASE (January 1980 to December 2015), Latin American and Caribbean Health Sciences (LILACS) (January 1982 to December 2015), the ISRCTN registry (www.isrctn.com/editAdvancedSearch), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 15 December 2015. We used the Science Citation Index and searched the reference lists of the included trials to identify relevant trials for this review. Selection criteria We included in this review randomized controlled trials (RCTs) comparing LASEK versus PRK for correction of myopia. Trial participants

  2. Acanthamoeba keratitis after photorefractive keratectomy.

    PubMed

    Kaldawy, Roger M; Sutphin, John E; Wagoner, Michael D

    2002-02-01

    A 37-year-old women developed severe suppurative keratitis immediately after having photorefractive keratectomy in her left eye. The keratitis was unresponsive to intensive topical antibiotic agents and topical and systemic steroids. Although the differential diagnosis included nonmicrobial and fungal keratitis, the clinical course and confocal microscopy suggested, and subsequent histopathologic examination confirmed, a diagnosis of Acanthamoeba keratitis. The amebic contamination probably resulted from exposure of the deepithelialized cornea to contaminated freshwater in a northern Wisconsin marsh. This case emphasizes the importance of encouraging patients with epithelial defects and bandage soft contact lenses to avoid exposure to contaminated freshwater until reepithelialization is complete.

  3. 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).

  4. Photorefractive Keratectomy for Residual Myopia after Myopic Laser In Situ Keratomileusis

    PubMed Central

    Fouda, Sameh M.

    2017-01-01

    Purpose. To evaluate the safety, efficacy, and predictability of photorefractive keratectomy (PRK) on the corneal flap for correction of residual myopia following myopic laser in situ keratomileusis (LASIK). Patients and Methods. A retrospective study on eyes retreated by PRK on the corneal flap for residual myopia after LASIK. All eyes had no enough stroma after LASIK sufficient for LASIK enhancement. Data included spherical equivalent (SE), uncorrected and best corrected visual acuity (UCVA and BCVA), central pachymetry, corneal higher order aberrations (HOAs), corneal hysteresis (CH), corneal resistance factor (CRF), and corneal haze. Results. The study included 64 eyes. Before PRK, the mean central pachymetry was 400.21 ± 7.8 μm, the mean SE was −1.74 ± 0.51 D, and the mean UCVA and BCVA were 0.35 ± 0.18 and 0.91 ± 0.07, respectively. 12 months postoperatively, the mean central corneal thickness was 382.41 ± 2.61 μm, the mean SE was −0.18 ± 0.32 D (P < 0.01), and the mean UCVA and BCVA were 0.78 ± 0.14 (P = 0.01) and 0.92 ± 0.13 (P > 0.5), respectively. The safety index was 1.01 and the efficacy index was 0.86. No significant change was observed in corneal HOAs. Conclusions. Residual myopia less than 3 D after LASIK could be safely and effectively treated by PRK and mitomycin C with a high predictability. This prevents postoperative ectasia and avoids the flap related complications but has no significant effect on HOAs. PMID:28168049

  5. Effect of beam variables on corneal sensitivity after excimer laser photorefractive keratectomy

    PubMed Central

    Lawrenson, J.; Corbett, M.; O'Brart, D.; Marshall, J.

    1997-01-01

    AIM—To investigate changes in corneal touch sensitivity following excimer laser photorefractive keratectomy (PRK) using different beam configurations.
METHODS—20 subjects were given a unilateral −3.00 D correction with either a 5 mm (26 µm, n=10) or 6 mm (42 µm, n=10) beam diameter. Thirty subjects underwent a unilateral −6.00 D correction with 5 mm (62 µm, n=10), 6 mm (78 µm, n=10), or multizone (62 µm, n=10) treatments. The multizone treatment was 6 mm in diameter with the depth of the 5 mm treatment. Corneal sensitivity was measured using a slit-lamp mounted Cochet-Bonnet aesthesiometer before and at 1, 3, 6, and 12 months after PRK. Stimulus locations included points lying within the ablated zone (central) and outside (peripheral). These were compared with the equivalent locations in control (untreated) eyes.
RESULTS—There was a significant reduction in corneal sensitivity within the central (ablated) zone in all treatment groups after PRK. In most groups a return to full sensitivity was achieved by 6 months with the exception of the multizone treatment group which showed significant corneal hypoaesthesia at 12 months. Peripheral corneal sensitivity was also reduced in this group up to 3 months after the procedure. A comparison between the −3.00 D and −6.00 D treatment groups showed no significant difference. However, combining data from all treatment groups, a significant correlation was found between the interocular difference in central corneal sensitivity and postoperative haze at 3 and 6 months.
CONCLUSIONS—For corrections up to −6.00 D ablation depth and treatment zone diameter do not appear to be clinically important determinants of corneal hypoaesthesia. In contrast, postoperative corneal haze appears to correlate with sensitivity loss.

 PMID:9349159

  6. Orthoptic Changes following Photorefractive Keratectomy

    PubMed Central

    Rajavi, Zhale; Nassiri, Nader; Azizzadeh, Monir; Ramezani, Alireza; yaseri, Mehdi

    2011-01-01

    Purpose To report orthoptic changes after photorefractive keratectomy (PRK). Methods This interventional case series included 297 eyes of 150 patients scheduled for PRK. Complete ophthalmologic evaluations focusing on orthoptic examinations were performed before and 3 months after PRK. Results Before PRK, 2 (1.3%) patients had esotropia which remained unchanged; 3 (2%) patients had far exotropia which improved after the procedure. Of 12 cases (8%) with initial exotropia at near, 3 (2%) cases became orthophoric, however 6 patients (4%) developed new near exotropia. A significant reduction in convergence and divergence amplitudes (P < 0.001) and a significant increase in near point of convergence (NPC) (P < 0.006) were noticed after PRK. A reduction ≥ 10 PD in convergence amplitude and ≥ 5 PD in divergence amplitude occurred in 10 and 5 patients, respectively. Four patients had initial NPC > 10 cm which remained unchanged after surgery. Out of 9 (6%) patients with baseline stereopsis > 60 seconds of arc, 2 (1.33%) showed an improvement in stereopsis following PRK. No patient developed diplopia postoperatively. Conclusion Preexisting strabismus may improve or remain unchanged after PRK, and new deviations can develop following the procedure. A decrease in fusional amplitudes, an increase in NPC, and an improvement in stereopsis may also occur after PRK. Preoperative evaluation of orthoptic status for detection of baseline abnormalities and identification of susceptible patients seem advisable. PMID:22454717

  7. PHOTOREFRACTIVE KERATECTOMY FOR ANISOMETROPIC AMBLYOPIA IN CHILDREN

    PubMed Central

    Paysse, Evelyn A

    2004-01-01

    ABSTRACT Purpose To assess the safety and efficacy of photorefractive keratectomy (PRK) in children with anisometropic amblyopia and to define the characteristics of children who may be candidates for PRK. Methods This thesis comprises four parts: (1) a retrospective analysis of risk factors predictive of amblyopia treatment failure in 104 children, (2) a prospective study of pachymetry in 198 eyes of 108 children, (3) development and implementation of a protocol to perform PRK under general anesthesia, and (4) a prospective interventional case-comparison study of PRK in 11 noncompliant children with anisometropic amblyopia to evaluate safety and long-term outcomes. Compliant and noncompliant children with anisometropic amblyopia were analyzed as controls. Results Factors associated with conventional anisometropic amblyopia treatment failure were poor compliance (P = .004), age 6 years or older (P = .01), astigmatism ≥1.5 diopters (P = .0002), and initial visual acuity of 20/200 or worse (P = .02). Central and paracentral pachymetry measurements were similar to published adult values. The general anesthesia protocol was efficient, and the laser functioned properly in all cases. All children did well with no anesthesia-related or treatment-related complications. Two years following PRK, the mean reduction in refractive error was 9.7 ± 2.6 diopters for myopes (P = .0001) and 3.4 ± 1.3 diopters for hyperopes (P = .001). The cycloplegic refractive error in 9 of 11 treated eyes was within 3 diopters of that in the fellow eye. Uncorrected visual acuity in the amblyopic eye improved by ≥2 lines in seven of nine children; best-corrected visual acuity improved by ≥2 lines in six of nine children. Stereopsis improved in five of nine children. The mean visual acuity of the PRK patients at last follow-up was significantly better than that of noncompliant controls (P = .003). The safety and efficacy indices for PRK in this study were 1.24 and 1.12, respectively

  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. Transepithelial Photorefractive Keratectomy for Low to Moderate Myopia in Comparison with Conventional Photorefractive Keratectomy

    PubMed Central

    Naderi, Mostafa; Jadidi, Khosrow; Mosavi, Seyed Aliasghar; Daneshi, Seyed Aref

    2016-01-01

    Purpose: To compare the effectiveness, safety and stability of the results of transepithelial photorefractive keratectomy (tPRK) with conventional photorefractive keratectomy (PRK) for low to moderate myopia. Methods: In this prospective non-randomized case-control study, patients with low to moderate myopia were assigned to the tPRK group (cases) or the PRK group (controls). In the tPRK group, eyes were treated using the Amaris excimer laser (SCHWIND eye-tech-solutions GmbH and Co. KG, Germany). Outcome measures included postoperative pain using McGill Pain Questionnaire, epithelial healing time, uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), manifest refraction, and safety and efficacy indexes which were compared between the study groups. Results: Three hundred forty eyes of 170 patients were enrolled in this study. Each study group comprised of 170 eyes of 85 patients. There was a significant difference between the two groups regarding the postoperative pain scores in favor of the tPRK group (P = 0.04). The tPRK group had a shorter epithelial healing time than the conventional PRK group postoperatively (P = 0.01). Mean UCVA was significantly better in the case group than in the control group at the postoperative month 2 (P = 0.01). Regarding the safety and efficacy indexes, the tPRK group had better results than the conventional PRK group (P < 0.01 for both comparisons). Conclusion: Transepithelial PRK seems to be superior to conventional PRK for treatment of low to moderate myopia in terms of postoperative pain, epithelial healing time, visual recovery and safety and efficacy indexes. PMID:27994803

  10. Comparison of laser in situ ketatomileusis and photorefractive keratectomy for myopia using a mixed-effects model

    PubMed Central

    Mori, Yosai; Miyata, Kazunori; Ono, Takashi; Yagi, Yusuke; Kamiya, Kazutaka; Amano, Shiro

    2017-01-01

    Purpose To compare the results of laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) for myopia using a mixed-effects model. Methods This comparative retrospective study was conducted in 1,127 eyes of 579 patients after LASIK and 270 eyes of 144 patients after PRK who had two or more postoperative follow-ups after 3 months. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refractive spherical equivalent (MRSE), percentage of eyes within ± 0.5 diopters (D) and ± 1.0 D of targeted refraction, and central corneal thickness were compared between PRK and LASIK groups using a mixed-effects model. Results Compared with the LASIK group, UCVA in the PRK group was significantly worse in the initial year but was significantly better after 4 years. The average BSCVA was not significantly different between the LASIK and PRK groups after 4 years. The average gain of BSCVA in the PRK group was significantly larger than that of the LASIK group after 2 years. MRSE in the LASIK and PRK groups showed a gradual myopic shift until 6 years after surgery. After 6 years, MRSE in the PRK group remained stable whereas MRSE in the LASIK group continued a myopic shift. The percentages of eyes within ± 0.5 D or ± 1.0 D in the LASIK group were significantly higher than those in the PRK group at 3 months but were significantly lower than those in the PRK group at 10 years. Conclusions PRK for myopia shows better efficacy than LASIK for myopia after 4 years. PMID:28362808

  11. 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

  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.

  13. Contact lens fitting after photorefractive keratectomy.

    PubMed Central

    Astin, C. L.; Gartry, D. S.; McG Steele, A. D.

    1996-01-01

    AIMS/BACKGROUND: This study evaluated contact lens fitting and the longer term response of the photorefractive keratectomy (PRK) cornea to lens wear. In PRK for myopia problems such as regression, anterior stromal haze, irregular astigmatism, halo aberration, and anisometropia have been reported. Certain patients therefore require contact lens correction to obtain best corrected visual acuity (BCVA). METHOD: From an original cohort of 80 patients, 15 were dissatisfied with their visual outcome 6 months after PRK. Ten of these were fitted with lenses and monitored regularly. RESULTS: The best fit rigid gas permeable lens of diameter 9.20-10.00 mm was generally 0.10 mm steeper than mean keratometry readings. Because of lid discomfort five patients were refitted with daily wear soft lenses. All 10 achieved satisfactory lens wear of 10 hours per day. Central corneal steepening of 0.75 D (0.15 mm) occurred in one patient. Two patients had slight central corneal flattening. Three patients discontinued lens wear as they found lens care a nuisance. Four finally opted for retreatment by PRK. CONCLUSIONS: In most cases, contact lenses gave good visual acuity and, in cases of mild irregular astigmatism, a significant improvement over spectacle BCVA. No significant adverse reaction to contact lens wear was found. Although ocular tolerance of lenses was satisfactory, several patients discontinued lens wear or sought improved unaided vision. Images PMID:8795370

  14. 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.

  15. Effect of contact lens wear on photorefractive keratectomy.

    PubMed

    Gimbel, H V; Sun, R

    1993-10-01

    This study compares refractive effect and epithelial healing after photorefractive keratectomy among patients who wore contact lenses before surgery versus those who wore glasses before surgery. Data were reviewed on 130 photorefractive keratectomy cases at the 1-week, 2-week, and 4- to 6-month postoperative visits. The patients were divided into three groups based on whether or not they wore contact lenses before surgery: 1) rigid gas permeable lens wearers; 2) soft lens wearers; 3) no contact lens wear. There were no significant differences in epithelial healing among the groups. Some regression of refractive effect was observed both in mean spherical equivalent and in mean keratometry in all the groups from 2 weeks to 6 months postoperatively. There was no significant difference in the regression of each group. In addition, the changes of spherical equivalent and keratometry before surgery and 4 to 6 months after surgery were compared among the groups with no significant differences. Based upon these results, we conclude that contact lens wearing does not seem to influence epithelial healing after photorefractive keratectomy surgery and also does not affect the refractive effect in the early postoperative period.

  16. 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

  17. Successful Surgical Correction of Astigmatism using Customized Ablation Photorefractive Keratectomy

    PubMed Central

    TAHERI, Hakimeh; RAMIN, Shahrokh

    2016-01-01

    The aim of this study was to determine the change in the degree of astigmatism in patients treated with customized ablation photorefractive keratectomy (PRK). This is a cross-sectional study that involved 92 otherwise healthy subjects with regular and irregular astigmatism ≥ 1.25 D (mean age: 39.09 ± 7.72 years; range: 20–59 years). All study subjects were treated with customized ablation PRK using a Technolas 217p Excimer Laser System. Before and 6 months after the surgery, a refraction assessment was conducted for each subject, and the effectiveness of the surgery for correcting astigmatism was evaluated. There was a significant change in astigmatism based on the results of an automated refraction exam of -1.67 ± 1.03 D (P < 0.001), from -2.51 ± 1.45 D preoperatively to -0.87 ± 0.94 D postoperatively. There was also a significant change in subjective refraction of -2.00 ± 1.25 D (P < 0.001), from -2.46 ± 1.52 D preoperatively to -0.46 ± 0.97 D postoperatively. Therefore, our results show that customized ablation PRK is effective for correcting astigmatism ≥ 1.25 D (P < 0.001). PMID:28293648

  18. Photorefractive keratectomy for myopia and myopic astigmatism correction using the WaveLight Allegretto Wave Eye-Q excimer laser system.

    PubMed

    Costa, Esmeralda; Franqueira, Nuno; Rosa, Andreia M; Tavares, Cristina; Quadrado, Maria J; Lobo, Conceição; Murta, Joaquim N

    2014-06-01

    To analyze photorefractive keratectomy (PRK) outcomes in myopia and myopic astigmatism correction using the WaveLight Allegretto Wave Eye-Q(®) excimer laser system (WaveLight Laser Technologie AG, Erlangen, Germany). 222 eyes of 151 patients underwent PRK (mean age 33.5 ± 6.8 years). Pre-operative best spectacle-corrected visual acuity (BSCVA) ranged from 0.4 to -0.1 logMAR (mean -0.03 ± 0.06). Mean spherical equivalent (SE) was -3.29 ± 1.20 D. Efficacy, predictability and safety were evaluated. Minimum follow-up was 3 months. Accountability at 3 and 6 months was 100 and 54 %, respectively (median follow-up 5 months, mean 5.2 ± 2.6 months). At 3 months, mean uncorrected visual acuity (UCVA) was -0.02 ± 0.07 logMAR, BSCVA -0.03 ± 0.05 logMAR, efficacy index 0.98 and safety index 1.02. UCVA was ≥20/16 in 40.1 %, ≥20/20 in 86.5 % and ≥20/25 in 98.2 %. Mean SE was -0.02 ± 0.20 D. Residual refractive error was ± 0.13 D in 81.5 %, ± 0.25 D in 88.7 % and ± 0.50 D in 97.7 %. At 6 months, outcomes were similar: mean UCVA was -0.02 ± 0.07 logMAR, BSCVA -0.03 ± 0.06 logMAR, efficacy index 1.00 and safety index 1.03. UCVA was ≥20/16 in 43.7 %, ≥20/20 in 86.6 % and ≥20/25 in 96.6 %. Mean SE was -0.02 ± 0.17 D. Residual refractive error was ± 0.13 D in 86.6 %, ± 0.25 D in 93.3 % and ± 0.50 D in 98.3 %. Refractive stability was achieved at 3 months. No patient lost more than one line of BSCVA. There were no retreatments. The WaveLight Allegretto Wave Eye-Q is effective, predictable and safe in low-to-moderate myopia and myopic astigmatism PRK correction.

  19. Photorefractive Keratectomy with Adjunctive Mitomycin C for Residual Error after Laser-Assisted In Situ Keratomileusis Using the Pulzar 213 nm Solid-State Laser: Early Results.

    PubMed

    Ng-Darjuan, Maya Fe; Evangelista, Raymond P; Agahan, Archimedes Lee D

    2013-01-01

    Purpose. To evaluate the accuracy, efficacy, stability, and safety of photorefractive keratectomy (PRK) enhancement using the Pulzar 213 nm solid-state laser (SSL) with adjunctive Mitomycin C in eyes previously treated with laser assisted in situ keratomileusis (LASIK) with residual error of refraction. Methods. This is a prospective noncomparative case series of 16 eyes of 12 patients who underwent PRK for residual refractive error after primary LASIK. Mitomycin C 0.02% was used after the PRK to prevent haze formation. Outcomes measured were pre- and postoperative manifest refraction spherical equivalent (MRSE), uncorrected (UDVA) and best-corrected distance visual acuity (CDVA), and slit lamp evidence of corneal complications. Results. The mean UDVA improved from 20/70 preoperatively to 20/30 postoperatively. The average gain in lines for the UDVA was 2.38. After six months of followup, the postoperative MRSE within 0.50 D in 56% (9) of eyes and 94% (15) eyes were within 1.0 diopters of the intended correction. No eyes developed haze all throughout the study. Conclusion. PRK enhancement with adjunctive use of Mitomycin C for the correction of residual error of refraction after LASIK using the Pulzar 213 nm solid-state laser is an accurate, effective, and safe procedure.

  20. Comparison of Loteprednol with Fluorometholone after Myopic Photorefractive Keratectomy

    PubMed Central

    Karimian, Farid; Faramarzi, Amir; Fekri, Sahba; Mohammad-Rabie, Hossein; Najdi, Danial; Doozandeh, Azadeh; Delfaza-Baher, Siamak; Yaseri, Mehdi

    2017-01-01

    Purpose: To compare the efficacy and side effects of loteprednol versus fluorometholone after myopic photorefractive keratectomy (PRK). Methods: One hundred and twenty four eyes of 62 patients who underwent PRK were enrolled in this study. One eye of each subject was randomized to receive loteprednol 0.5% and the fellow eye was given fluorometholone 0.1%. Patients were followed up for three months. Results: There was no significant difference in uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction, corneal haze, intraocular pressure (IOP), and ocular discomfort and redness between groups at the final visit. At 3 months postoperatively, 20/25 or better UDVA was achieved in 95% of the loteprednol group and 92% of the fluorometholone group (P > 0.05). There was neither visually significant corneal haze nor ocular hypertension (IOP rise > 10 mmHg or IOP > 21 mmHg) in any group. Conclusion: The efficacy and side effects of loteprednol 0.5% and fluorometholone 0.1% after myopic PRK are comparable. PMID:28299001

  1. Multiphoton Imaging of Rabbit Cornea Treated with Mitomycin C after Photorefractive Keratectomy

    NASA Astrophysics Data System (ADS)

    Hsueh, Chiu-Mei; Lo, Wen; Wang, Tsung-Jen; Hu, Fung-Rong; Dong, Chen-Yuan

    2007-07-01

    In this work we use multiphoton microscopy to observe the post surgery structure variation of rabbit cornea after photorefractive keratectomy (PRK). In addition, we added mitomycin C (MMC) to the post surgery rabbit cornea in order to investigate the effect of MMC treatment on the postoperative regeneration.

  2. Prospective Evaluation of Mesopic Night Vision and Night Vision Goggle Visual Acuity After Photorefractive Keratectomy (PRK)

    DTIC Science & Technology

    2005-03-01

    DTIC) should direct requests for copies to: Defense Technical Information Center, 8725 John J. Kingman Rd., STE 0944, Ft. Belvior, VA 22060-6218. Non...770-6. 9. Verdon W, Bullimore M, Maloney RK. Visual Performance after Photorefractive Keratectomy. A Prospective Study. Arch Ophthalmol. December

  3. Effect of Mitomycin C on Myopic versus Astigmatic Photorefractive Keratectomy

    PubMed Central

    Fawzy, Samah M.

    2017-01-01

    Purpose. Long-term mitomycin C (MMC) effects on photorefractive keratectomy (PRK) were compared in simple myopic and astigmatic patients. Methods. In this observational cohort study, subjects were selected based on preoperative and postoperative data collected from medical records; they were divided into simple myopia with/without MMC and myopic astigmatism with/without MMC groups. Haze, uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), subjective refraction, and K-reading were evaluated at 1-, 3-, 6-, and 12-month follow-ups. Results. One hundred fifty-nine eyes of 80 subjects (34 women and 46 men; mean age, 26.81 ± 7.74 years; range, 18–53 years; spherical powers, −0.50 to −8.00 DS; and cylindrical powers, −0.25 to −5.00 DC) were enrolled. One year postoperatively, the simple myopia with/without MMC groups showed no difference in UCVA (P = 0.187), BCVA (P = 0.163), or spherical equivalent (P = 0.163) and a significant difference (P = 0.0495) in K-reading; the haze formation difference was nonsignificant (P = 0.056). Astigmatic groups with/without MMC showed a significant difference in K-reading (P < 0.0001). MMC groups had less haze formation (P < 0.0001). Conclusion. PRK with intraoperative MMC application showed excellent visual outcomes. MMC's effect on astigmatic patients was significantly better with acceptable safety and minimal side effects. PMID:28392938

  4. Effectiveness of scraping and mitomycin C to treat haze after myopic photorefractive keratectomy.

    PubMed

    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.

  5. Confocal microscopy reveals persisting stromal changes after myopic photorefractive keratectomy in zero haze corneas

    PubMed Central

    Bohnke, M.; Thaer, A.; Schipper, I.

    1998-01-01

    AIMS—Micromorphological examination of the central cornea in myopic patients 8-43 months after excimer laser photorefractive keratectomy (PRK), using the slit scanning confocal microscope.
METHODS—Patients were selected from a larger cohort of individuals on the basis of full corneal clarity (haze grading 0 to +1; mean 0.3) and their willingness to participate in the study. 15 eyes of 10 patients with myopic PRK (−4 to −11 D; mean 6.7) and an uneventful postoperative interval of 8-43 months (mean 26) were examined. Contact lenses had been worn by eight of the 10 patients for 4-11 years (mean 6.7) before surgery. Controls included the five untreated fellow eyes of PRK patients, 10 healthy, age matched volunteers without a history of ocular inflammation or contact lens wear, and 20 patients who had worn rigid gas permeable (n=10) or soft contact lenses (n=10) for 2-11 years. Subjects were examined with a real time flying slit, scanning confocal microscope using ×25 and ×50 objectives.
RESULTS—In PRK treated patients and contact lens wearers, basal layer epithelial cells sporadically displayed enhanced reflectivity. The subepithelial nerve plexus was observed in all individuals, but was usually less well contrasted in the PRK group, owing to the presence of a very discrete layer of subepithelial scar tissue, which patchily enhanced background reflectivity. Within all layers of the stroma, two distinct types of abnormal reflective bodies were observed in all PRK treated eyes, but in none of the controls. One had the appearance of long (>= 50 µm), slender (2-8 µm in diameter) dimly reflective rods, which sometimes contained bright, punctate, crystal-like inclusions, arranged linearly and at irregular intervals. The other was shorter (<25 µm), more slender in form (<1 µm in diameter), and highly reflective; these so called needles were composed of crystal-like granules in linear array, with an individual appearance similar to the bright

  6. Single-step transepithelial photorefractive keratectomy in high myopia: qualitative and quantitative visual functions

    PubMed Central

    Adib-Moghaddam, Soheil; Soleyman-Jahi, Saeed; Adili-Aghdam, Fatemeh; Arba Mosquera, Samuel; Hoorshad, Niloofar; Tofighi, Salar

    2017-01-01

    AIM To investigate quantitative and qualitative optical outcomes of single-step transepithelial photorefractive keratectomy (TransPRK) in high myopia. METHODS In a prospective interventional case-series, 30 eyes with high myopia (-6.00 to -8.75 D) with (up to -3.00 D) or without astigmatism were enrolled from Bina Eye Hospital, Tehran, Iran. One-step TransPRK was performed with aberration-free aspherical optimized profile and SCHWIND AMARIS 500 laser. One-year follow-up results for refraction, visual acuities, vector analysis, ocular wave-front (OWF) and corneal wave-front (CWF) higher order aberrations (HOA), contrast sensitivity (CS), and post-operative haze were assessed. RESULTS After the surgery, both photopic and mesopic CSs significantly improved (both P<0.001). We detected significant induction of OWF coma and trefoil (P<0.001 for both) HOAs; CWF coma (P=0.002), spherical (P<0.001), and tetrafoil (P=0.003) HOAs in 6 mm analysis diameter; and CWF trefoil (P=0.04) HOA in 4 mm analysis diameter. The range of mean induction observed for various HOAs was 0.005-0.11 µm. The 86.7% of eyes reached an uncorrected distance visual acuity of 20/20 or better; 96.7% of eyes were within ±0.5 D of targeted spherical refraction. In vector analysis, mean correction index value was 1.03 and mean index of success was 0.22. By 12mo after the operation, no eye lost any number of corrected distance visual acuity lines. We detected no corneal haze greater than 1+ throughout the follow-up. CONCLUSION Our findings show promising effects of single-step TransPRK on quality of vision in high myopic eyes. It also improves refraction and visual acuity. PMID:28393038

  7. Comparative evaluation of Comfilcon A and Senofilcon A bandage contact lenses after transepithelial photorefractive keratectomy

    PubMed Central

    Mukherjee, Achyut; Ioannides, Antonis; Aslanides, Ioannis

    2014-01-01

    Purpose To evaluate and compare Comfilcon A and Senofilcon A silicone hydrogel contact lenses used as a therapeutic bandage following transepithelial excimer laser photorefractive keratectomy (PRK). Methods Patients undergoing transepithelial PRK for myopia were prospectively recruited. Included patients had a Comfilcon A silicone hydrogel lens inserted in one eye, with a Senofilcon A lens in the contralateral eye. Postoperative assessment of subjective pain, epithelial healing and visual recovery was at day 1, 3 and 7. Contact lens factors including centration, movement and deposits were assessed. Results 48 eyes of 24 patients were included in the study. Mean age was 31 years (SD 11) and mean refractive error −4.5 D (SD 1.8). Mean pain score at day 1 was significantly higher in the Comfilcon group at 4.6 (SD 2.7) vs. 1.5 (SD2.5) in the Senofilcon group (P < 0.005). Mean time to healing was 3.17 days (SD 0.37) in the Comfilcon group, and 3.21 days (SD 0.4) in the Senofilcon group, with no difference in defect size. There was a pronounced central raphe in 1 eye in the Comfilcon group vs. 5 eyes in the Senofilcon group (P = 0.19). Significantly more eyes demonstrated no lens movement in the Senofilcon group (18 vs. 4, P = 0.0001). Conclusion The variation in material characteristics and lens geometry of different silicone hydrogel lenses affects their clinical characteristics in therapeutic roles. Other factors than oxygen permeability may affect pain and epithelial healing, with superior pain relief from the less permeable Senofilcon lens in this study. PMID:25649638

  8. Custom photorefractive keratectomy ablations for the correction of spherical and cylindrical refractive error and higher-order aberration.

    PubMed

    Schwiegerling, J; Snyder, R W

    1998-09-01

    Photorefractive keratectomy is an evolving refractive procedure for correcting myopia, hyperopia, and astigmatism. Earlier descriptions of the patterns required for this surgery are based on paraxial optics. In this investigation the required pattern is generalized to account for spherical refractive error (defocus), axial astigmatism of arbitrary orientation, and fourth-order aberrations of the eye. The patterns described in this study can be used to customize photorefractive keratectomy and to provide corrections that account for aberration content as well as paraxial values. Furthermore, a description of the pattern along the boundary of the optical zone is given, which may prove useful in designing blending zones. An example of the use of these techniques is given for a schematic eye model.

  9. A prospective, contralateral comparison of photorefractive keratectomy (PRK) versus thin-flap LASIK: assessment of visual function

    PubMed Central

    Hatch, Bryndon B; Moshirfar, Majid; Ollerton, Andrew J; Sikder, Shameema; Mifflin, Mark D

    2011-01-01

    Purpose: To compare differences in visual acuity, contrast sensitivity, complications, and higher-order ocular aberrations (HOAs) in eyes with stable myopia undergoing either photo-refractive keratectomy (PRK) or thin-flap laser in situ keratomileusis (LASIK) (intended flap thickness of 90 μm) using the VISX Star S4 CustomVue excimer laser and the IntraLase FS60 femtosecond laser at 1, 3, and 6 months postoperatively. Methods: In this prospective, masked, and randomized pilot study, refractive surgery was performed contralaterally on 52 eyes: 26 with PRK and 26 with thin-flap LASIK. Primary outcome measures were uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), contrast sensitivity, and complications. Results: At 6 months, mean values for UDVA (logMAR) were −0.043 ± 0.668 and −0.061 ± 0.099 in the PRK and thin-flap LASIK groups, respectively (n = 25, P = 0.466). UDVA of 20/20 or better was achieved in 96% of eyes undergoing PRK and 92% of eyes undergoing thin-flap LASIK, whereas 20/15 vision or better was achieved in 73% of eyes undergoing PRK and 72% of eyes undergoing thin-flap LASIK (P > 0.600). Significant differences were not found between treatment groups in contrast sensitivity (P ≥ 0.156) or CDVA (P = 0.800) at postoperative 6 months. Types of complications differed between groups, notably 35% of eyes in the thin-flap LASIK group experiencing complications, including microstriae and 2 flap tears. Conclusion: Under well-controlled surgical conditions, PRK and thin-flap LASIK refractive surgeries achieve similar results in visual acuity, contrast sensitivity, and induction of HOAs, with differences in experienced complications. PMID:21573091

  10. Intraocular Lens Calculation for Cataract Treated with Photorefractive Keratectomy Using Ray Tracing Method.

    PubMed

    Ishikawa; Hirano; Murai; Kumagai; Nakayasu; Kanai

    2000-09-01

    Purpose: Conventional methods (such as the SRK-II formula) do not accurately calculate the power of the intraocular lens (IOL) after refractive surgery. Therefore, we compared a new formula including a ray tracing method to the conventional method for foldable IOL lens implantation.Method: Foldable IOLs (MA 60 BM) were implanted in 26 patients (32 eyes) using the phakoemulsification technique. The power of the IOL was measured preoperatively using the SRK-II formula in all cases. From the results of postoperative refractive errors of these cases, the power of IOL calculated by the ray tracing method was compared to the SRK-II formula. Cataract patients first treated with photorefractive keratectomy (PRK) received IOL implants using our ray tracing method and their postoperative refraction was measured.Results: The average postoperative refractive error was 1.32 D in SRK-II formula, 0.95 D in the ray tracing method with Ray 1 used and 0.89 D with Ray 2 used. Postoperative refraction of both eyes first treated with PRK was -1.00 D.Conclusion: The average postoperative refractive error was reduced in the ray tracing method using Olsen's predicted ACD (Ray 2) compared to SRK-II formula. This new tracing method appears to be useful for determination of IOL power and it may be applied for IOL calculation for cataract surgery after refractive surgery.

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

    PubMed Central

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

    2015-01-01

    Abstract 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

  12. 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

  13. Assessment of contrast sensitivity and aberrations after photorefractive keratectomy in patients with myopia greater than 5 diopters.

    PubMed

    Fahim, Alireza; Rezvan, Bijan; Hashemi, Hassan

    2013-09-09

    This study aimed to assess changes in contrast sensitivity and aberrations in cases of myopia greater than 5.0 diopter (D) who had photorefractive keratectomy (PRK). In this semi-experimental study, 20 eyes of ten patients were studied. Inclusion criteria were at least 5.0 D of myopia, stable refraction in the past year, no history of refractive surgery, a minimum corneal thickness of 480 μm, and having surgery in both eyes. Exclusion criteria were the presence of any corneal condition. In addition to the routine tests, aberrometry and assessment of contrast sensitivity was done using the WaveLight Allegro Analyzer and the VectorVision CSV-1000. After PRK using the Concerto Excimer Laser (WaveLight, Alcon), patients were scheduled to have follow-up visits at 1 month, 3 months, and 1 year after surgery. Contrast sensitivity with glare showed an increasing trend only at the spatial frequency of 3 cycles per degree (cpd) (P=0.013). Contrast sensitivity without glared increased postoperatively at special frequencies of 3, 6, and 18 cpd (P<0.05). The preoperative level of higher order aberrations root mean square (HOA RMS) of 0.24±0.08 reached 0.71±0.25 at 12 months after surgery. Assessment of comma and trefoil showed no significant difference between preoperative and postoperative values, but the amount of spherical aberration changed from a mean preoperative value of 0.0±0.09 to 0.27±0.15 at 12 months after surgery. In the treatment of myopia greater than 5.0 D, PRK with the Concerto Excimer Laser can improve contrast sensitivity in certain spatial frequencies. This is while HOA RMS and spherical aberration increase.

  14. Comparison of Changes in Corneal Biomechanical Properties after Photorefractive Keratectomy and Small Incision Lenticule Extraction

    PubMed Central

    Yıldırım, Yusuf; Ölçücü, Onur; Başcı, Abdurrahman; Ağca, Alper; Özgürhan, Engin Bilge; Alagöz, Cengiz; Demircan, Ali; Demirok, Ahmet

    2016-01-01

    Objectives: To compare the postoperative biomechanical properties of the cornea after photorefractive keratectomy (PRK) and small incision lenticule extraction (SMILE) in eyes with low and moderate myopia. Materials and Methods: We retrospectively examined 42 eyes of 23 patients undergoing PRK and 42 eyes of 22 patients undergoing SMILE for the correction of low and moderate myopia. Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured with an Ocular Response Analyzer before and 6 months after surgery. We also investigated the relationship between these biomechanical changes and the amount of myopic correction. Results: In the PRK group, CH was 10.4±1.3 mmHg preoperatively and significantly decreased to 8.5±1.3 mmHg postoperatively. In the SMILE group, CH was 10.9±1.7 mmHg preoperatively and decreased to 8.4±1.5 mmHg postoperatively. CRF was significantly decreased from 10.8±1.1 mmHg to 7.4±1.5 mmHg in the PRK group whereas it was decreased from 11.1±1.5 mmHg to 7.9±1.6 mmHg in the SMILE group postoperatively. There was a significant correlation between the amount of myopic correction and changes in biomechanical properties after PRK (r=-0.29, p=0.045 for CH; r=-0.07, p=0.05 for CRF) and SMILE (r=-0.25, p=0.048 for CH; r=-0.37, p=0.011 for CRF). Conclusion: Both PRK and SMILE can affect the biomechanical strength of the cornea. SMILE resulted in larger biomechanical changes than PRK. PMID:27800259

  15. Corneal Epithelial Remodeling and Its Effect on Corneal Asphericity after Transepithelial Photorefractive Keratectomy for Myopia

    PubMed Central

    Zheng, Xiuyun

    2016-01-01

    Purpose. To evaluate the changes in epithelial thickness profile following transepithelial photorefractive keratectomy (T-PRK) for myopia and to investigate the effect of epithelial remodeling on corneal asphericity. Methods. Forty-four patients (44 right eyes) who underwent T-PRK were retrospectively evaluated. Epithelial thickness was measured using spectral-domain optical coherence tomography at different corneal zones (central, 2 mm; paracentral, 2–5 mm; and mid-peripheral, 5-6 mm) preoperatively and at 1 week and 1, 3, and 6 months postoperatively. The correlation between the changes in corneal epithelial thickness (ΔCET) and postoperative Q-value changes (ΔQ) was analyzed 6 months postoperatively. Results. Epithelial thickness at 6 months showed a negative meniscus-like lenticular pattern with less central thickening, which increased progressively toward the mid-periphery (3.69 ± 4.2, 5.19 ± 3.8, and 6.23 ± 3.9 μm at the center, paracenter, and mid-periphery, resp., P < 0.01). A significant positive relationship was observed between epithelial thickening and ΔQ 6 months postoperatively (r = 0.438, 0.580, and 0.504, resp., P < 0.01). Conclusions. Significant epithelial thickening was observed after T-PRK and showed a lenticular change with more thickening mid-peripherally, resulting in increased oblateness postoperatively. Epithelial remodeling may modify the epithelial thickness profile after surface ablation refractive surgery for myopia. PMID:27672447

  16. Corneal wound healing after photorefractive keratectomy: a 3-year confocal microscopy study.

    PubMed Central

    Erie, Jay C

    2003-01-01

    PURPOSE: To perform a sequential quantitative analysis of corneal wound healing after photorefractive keratectomy (PRK) by using confocal microscopy in vivo. METHODS: In a prospective, nonrandomized, comparative trial performed in an institutional setting, 24 eyes of 14 patients received PRK to correct refractive errors between -1.25 and -5.75 D. Central corneas were examined preoperatively and at 1 day, 5 days, and 1, 3, 6, 12, 24, and 36 months after PRK by using confocal microscopy. A masked observer randomly examined 3 to 6 confocal scans per eye per visit to determine epithelial and stromal thickness, keratocyte density in 5 anterior-posterior stromal layers, corneal nerve density in the subbasal region and the stroma, and corneal light backscattering (corneal haze). RESULTS: Epithelial thickness increased 21% (P < .001) by 12 months after PRK and thereafter remained unchanged to 36 months after PRK. There was no change in stromal thickness between 1 and 36 months after PRK (P = .35). The dense keratocyte population in the preoperative anterior 10% of the stroma (32,380 +/- 5,848 cells/mm3) that was partially or completely removed during photoablation was not reconstituted at 36 months in the anterior 10% of the post-PRK stroma (17,720 +/- 4,308 cells/mm3, P < .001). Subbasal nerve fiber bundle density was decreased 60% at 12 months after PRK (P < .001) before returning to densities at 24 and 36 months after PRK that were not significantly different from preoperative values (P = 1.0). Activated keratocytes and corneal haze peaked at 3 months after PRK. CONCLUSIONS: Wounding of the cornea by PRK alters the normal structure, cellularity, and innervation of the cornea for up to 36 months. PMID:14971584

  17. Photorefractive Keratectomy (PRK) is Safe and Effective for Patients with Myopia and Thin Corneas

    PubMed Central

    NADERI, Mostafa; GHADAMGAHI, Saeed; JADIDI, Khosrow

    2016-01-01

    The aim of this study was to evaluate the long-term safety and efficacy of photorefractive keratectomy (PRK) for patients with myopia and thin corneas. In this retrospective case series, we included 74 eyes of 38 patients with myopia and central corneal thickness (CCT) < 550 µm who underwent PRK and had a mean postoperative follow-up period of four years. The following factors were evaluated: CCT, refraction, uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), ablation depth, safety and efficacy indices (i.e., the ratio of the mean postoperative BCVA to the mean preoperative BCVA, and the ratio of the mean postoperative UCVA to mean preoperative the BCVA, respectively), and evidence of corneal ectasia (based on Orbscan topography images).The patients were aged 20 – 46 years (mean ±SD age, 28.18± 6.82 years). The mean ± SD pre- and postoperative CCTwas485.92 ± 9.27 µm and 434.84 ± 20.48 µm, respectively. The mean ± SD pre- and postoperative myopia was -2.77 D ± 1.51 and -0.24 ± 0.39 D, respectively, and the mean ± SD pre- and postoperative astigmatism was -0.82 D ± 0.99 and -0.37 ± 0.37 D, respectively. The mean pre- and postoperative BCVA and postoperative UCVA was 0.011 ± 0.03 Logarithm of the Minimum Angle of Resolution (log MAR), 0.003 ± 0.01 log MAR, and 0.054 ± 0.09 log MAR, respectively. The mean ± SD ablation depth, safety index and efficacy index was 54.34 ± 16.28 µm, 0.02 ± 0.12, and 0.11 ± 0.50, respectively. Regarding the postoperative corneal clarity, 72 eyes (97.3%) had a clear cornea (grade 0) and the remaining two eyes of one patient (2.70%) had a trace haze (grade 1). There was no evidence of corneal ectasia on any of the Orbscan topography images. Thus, among patients with myopia and thin corneas (<500 µm), PRK seems to be acceptable in terms of both safety and efficacy 4 years after surgery, based on the stability of postoperative refraction, visual acuity, and topographic outcomes, and outcomes based on

  18. [The effect of tranilast on subepithelial corneal opacity after excimer laser keratectomy].

    PubMed

    Sakai, T; Okamoto, S; Iwaki, Y

    1997-10-01

    Recent studies have reported that tranilast inhibited in vitro the proliferation of keratocytes from corneal subepithelial opacities (haze) and collagen synthesis in cultured corneas after excimer laser photorefractive keratectomy (PRK). In this study 0.5% tranilast eye drops, 0.1% betametazone phosphate eyedrops, and a 0.5% tranilast base solution (control) were administered four times daily to rabbits which had undergone PRK. Weekly evaluation of the inhibitory effect of these drugs on haze began two weeks after surgery according to Fantes' classification. 0.5% tranilast suppressed haze from six weeks to thirteen weeks after PRK (p < 0.05). 0.1% betametazone phosphate showed no effect. These results suggested that 0.5% tranilast had a satisfactory therapeutic effect on haze after PRK.

  19. Label-free structural characterization of mitomycin C-modulated wound healing after photorefractive keratectomy by the use of multiphoton microscopy

    NASA Astrophysics Data System (ADS)

    Lo, Wen; Wang, Tsung-Jen; Chen, Wei-Liang; Hsueh, Chiu-Mei; Chen, Shean-Jen; Chen, Yang-Fang; Chou, Hsiu-Chu; Lin, Pi-Jung; Hu, Fung-Rong; Dong, Chen-Yuan

    2010-05-01

    We applied multiphoton autofluorescence (MAF) and second-harmonic generation (SHG) microscopy to monitor corneal wound healing after photorefractive keratectomy (PRK). Our results show that keratocyte activation can be observed by an increase in its MAF, while SHG imaging of corneal stroma can show the depletion of Bowman's layer after PRK and the reticular collagen deposition in the wound healing stage. Furthermore, quantification of the keratocyte activation and collagen deposition in conjunction with immunohistochemistry and histological images demonstrate the effectiveness of mitomycin C (MMC) in suppressing myofibroblast proliferation and collagen regeneration in the post-PRK wound healing process.

  20. 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

  1. Evaluation of the prophylactic use of mitomycin-C to inhibit haze formation after photorefractive keratectomy in high myopia: a prospective clinical study

    PubMed Central

    Hashemi, Hassan; Taheri, Seied Mohammad Reza; Fotouhi, Akbar; Kheiltash, Azita

    2004-01-01

    Background To study the effect of prophylactic application of mitomycin-C on haze formation in photorefractive keratectomy (PRK) for high myopia. Methods Fifty-four eyes of 28 myopic patients were enrolled in this prospective study. All eyes were operated by PRK followed by 0.02% mitomycin-C application for two minutes and washed with 20 ml normal saline afterwards. All eyes were examined thoroughly on the first 7 days and one month after surgery; 48 eyes (88.9%) at 3 and 6 months postoperatively. Hanna grading (in the scale of 0 to 4+) was used for assessment of corneal haze. Results The mean spherical equivalent refraction (SE) was -7.08 diopters (D) ± 1.11 (SD) preoperatively. Six months after surgery, 37 eyes (77.1%) achieved an uncorrected visual acuity (UCVA) of 20/20 or better, all eyes had a UCVA of 20/40 or better and 45 (93.7%) eyes had an SE within ± 1.00D. One month postoperatively, 2 eyes (3.7%) had grade 0.5+ of haze, while at 3 and 6 months after surgery no visited eye had haze at all. All eyes had a best corrected visual acuity (BCVA) of 20/40 or better and there were no lost lines in BCVA by 6 months after surgery. In spatial frequencies of 6 and 12 cycles per degree contrast sensitivity had decreased immediately after PRK and it had increased 1.5 lines by the 6th postoperative month compared to the preoperative data. Conclusions The results show the efficacy of mitomycin-C in preventing corneal haze after treatment of high myopia with PRK. This method- PRK + mitomycin-C – can be considered an alternative treatment for myopic patients whose corneal thicknesses are inadequate for laser in situ keratomileusis (LASIK). However, the results should be confirmed in longer follow-ups. PMID:15363107

  2. 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.

  3. Validity of Tono-pachymetry for Measuring Corrected Intraocular Pressure in Non-surgical and Post-photorefractive Keratectomy Eyes

    PubMed Central

    Hahn, In Kyun; Kim, Jae Yong; Kim, Myoung Joon; Tchah, Hungwon

    2017-01-01

    Purpose To assess the validity of central corneal thickness (CCT) and corrected intraocular pressure (IOP) values obtained by tono-pachymetry in non-surgical and post-photorefractive keratectomy (PRK) eyes. Methods For the study, 108 young healthy participants and 108 patients who had PRK were enrolled. Measurements were randomly performed by tono-pachymetry, ultrasonic (US) pachymetry, and Goldmann applanation tonometry (GAT). CCT measurement by tono-pachymetry was compared to that of US pachymetry. The corrected IOP value obtained by tono-pachymetry was compared to that obtained by US pachymetry and GAT. The corrected IOP from US pachymetry and GAT was calculated using the identical compensation formula built into the tono-pachymetry. Bland-Altman plot and paired t-test were conducted to evaluate the between-method agreements. Results The mean CCT measurement using tono-pachymetry was significantly greater by 7.3 µm in non-surgical eyes (p < 0.001) and 17.8 µm in post-PRK eyes (p < 0.001) compared with US pachymetry. Differences were significant in both Bland-Altman plotand paired t-test. The mean difference of corrected IOP values obtained by tono-pachymetry and calculated from measurements by US pachymetry and GAT was 0.33 ± 0.87 mmHg in non-surgical eyes and 0.57 ± 1.08 mmHg in post-PRK eyes. The differences in the Bland-Altman plot were not significant. Conclusions The CCT measurement determined using tono-pachymetrywas significantly thicker than that of US pachymetry. The difference in CCT was greater in post-PRK eyes than in non-surgical eyes. However, the corrected IOP value obtained by tono-pachymetry showed reasonable agreement with that calculated from US pachymetry and GAT measurements. PMID:28243023

  4. 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

  5. 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.

  6. 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

    2016-09-07

    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.

  7. Punctate keratopathy of West Indians in patients undergoing photorefractive surgery

    PubMed Central

    Galvis, Virgilio; Tello, Alejandro; Revelo, Mario L; Paredes, David; Jaramillo, Luis Carlos

    2013-01-01

    We present two cases of patients with corneal lesions compatible with punctate keratopathy of West Indians who underwent photorefractive keratectomy and laser-assisted in situ keratomileusis. Both had good postoperative results. The corneal lesions did not interfere with the refractive surgery. PMID:23355587

  8. Effect of the combination of basic fibroblast growth factor and cysteine on corneal epithelial healing after photorefractive keratectomy in patients affected by myopia

    PubMed Central

    Meduri, Alessandro; Scorolli, Lucia; Scalinci, Sergio Zaccaria; Grenga, Pier Luigi; Lupo, Stefano; Rechichi, Miguel; Meduri, Enrico

    2014-01-01

    Background: This study sought to evaluate the effect of basic fibroblast growth factor eye drops and cysteine oral supplements on corneal healing in patients treated with photorefractive keratectomy (PRK). Materials and Methods: One hundred and twenty patients treated bilaterally with PRK for myopia were enrolled at one of two eye centers (Clinica Santa Lucia, Bologna, Italy and Department of Ophthalmology, University of Magna Graecia, Catanzaro, Italy) and were treated at the former center. Sixty patients included in the study group (Group 1) were treated postoperatively with topical basic fibroblast growth factor plus oral L-cysteine supplements, whereas 60 subjects included in the control group (Group 2) received basic fibroblast growth factor eye drops. We recorded the rate of corneal re-epithelialization and patients were followed-up every 30 days for 6 months. Statistical analyses were performed on the collected data. Results: The eyes in Group 1 demonstrated complete re-epithelialization at Day 5, whereas the eyes in Group 2 achieved this status on Day 6. No side-effects were reported. Conclusions: Patients treated with basic fibroblast growth factor eye drops and L-cysteine oral supplements benefit from more rapid corneal re-epithelialization. In human eyes, this combination treatment appeared to be safe and effective in accelerating corneal surfacing after surgery. Financial Disclosure: No author has any financial or proprietary interest in any material or method used in this study. Trial Registration: Current Controlled Trials ISRCTN73824458. PMID:24145571

  9. The variant N363S of glucocorticoid receptor in steroid-induced ocular hypertension in Hungarian patients treated with photorefractive keratectomy

    PubMed Central

    Borgulya, Gábor; Filkorn, Tamás; Majnik, Judit; Bányász, Ilona; Nagy, Zoltán Zsolt

    2007-01-01

    Purpose Variation in sensitivity to glucocorticoids observed in healthy population is influenced by genetic polymorphisms of the glucocorticoid receptor gene (NR3C1). N363S, ER22/23EK, and Bcl I have been previously described as glucocorticoid-sensitivity modulating polymorphisms. We investigated whether these variants may contribute to steroid-induced ocular hypertension and if they play a role as protective or risk factors during exogenous glucocorticoid administration. Methods We examined 102 patients who underwent photorefractive keratectomy and received topical steroids (either fluorometholone 0.1% or prednisolone acetate 0.5% alone or combined) as part of postoperative therapy. The choice of steroid depended on course of wound healing and regression. Variations in intraocular pressure (IOP) levels in response to steroid therapy were observed. To genotype DNA, allele-specific PCR amplification was applied for the N363S polymorphism, and PCR-based restriction fragment length polymorphism analysis was performed to examine the Bcl I and the ER22/23EK polymorphisms. We separately analyzed data from three groups of patients: those who received fluorometholone only; those who were initially given fluorometholone then later switched to prednisolone acetate; and those who received prednisolone acetate only. Covariance analysis with forward stepwise variable selection was carried out. Results In cases where prednisolone acetate was administered, we found a significant correlation between N363S heterozygosity and steroid-induced ocular hypertension. ER22/23EK and Bcl I polymorphisms do not have a major influence on the risk of developing steroid-induced ocular hypertension. Conclusions Genotyping of high risk steroid responders may allow an individual therapy to avoid steroid-induced ocular hypertension. The N363S polymorphism may have a clinical significance in the future. PMID:17563720

  10. 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

  11. Excimer Laser Phototherapeutic Keratectomy for the Treatment of Clinically Presumed Fungal Keratitis

    PubMed Central

    Li, Liang-Mao; Zhao, Li-Quan; Qu, Ling-Hui; Li, Peng

    2014-01-01

    This retrospective study was to evaluate treatment outcomes of excimer laser phototherapeutic keratectomy (PTK) for clinically presumed fungal keratitis. Forty-seven eyes of 47 consecutive patients underwent manual superficial debridement and PTK. All corneal lesions were located in the anterior stroma and were resistant to medication therapy for at least one week. Data were collected by a retrospective chart review with at least six months of follow-up data available. After PTK, infected corneal lesions were completely removed and the clinical symptoms resolved in 41 cases (87.2%). The mean ablation depth was 114.39 ± 45.51 μm and diameter of ablation was 4.06 ± 1.07 mm. The mean time for healing of the epithelial defect was 8.8 ± 5.6 days. Thirty-four eyes (82.9%) showed an improvement in best spectacle-corrected visual acuity of two or more lines. PTK complications included mild to moderate corneal haze, hyperopic shift, irregular astigmatism, and thinning cornea. Six eyes (12.8%) still showed progressed infection, and conjunctival flap covering, amniotic membrane transplantation, or penetrating keratoplasty were given. PTK is a valuable therapeutic alternative for superficial infectious keratitis. It can effectively eradicate lesions, hasten reepithelialization, and restore and preserve useful visual function. However, the selection of surgery candidates should be conducted carefully. PMID:24891945

  12. Volumetric integration of photorefractive micromodifications in lithium niobate with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Paipulas, D.; Mizeikis, V.; Purlys, V.; ČerkauskaitÄ--, A.; Juodkazis, S.

    2015-03-01

    After the discovery that focused laser pulse is capable to locally change material's refractive index it became possible to integrate various photonic devices or data directly into the volume of transparent material, usually with conventional Direct Laser Writing (DLW) techniques. Many different photonic devices, passive or active, integrated in different materials were demonstrated. In majority of cased the change in refractive index comes from rearrangement (damage) of materials' lattice and are permanent. Metastable (reversible) modification can be beneficial for some applications and these could be realized in photorefractive crystals such as lithium niobate. While photorefractive data recording is a well studied process in holographic applications, the photorefractive induction via femtosecond laser pulses is scarcely investigated. in this work we demonstrate the possibility to form discrete regions for homogeneously-altered refractive index in bulk of pure and iron doped lithium niobate crystals using femtosecond DLW technique. We shoe that non-linear free charge generation and charge separation caused by the bulk photovoltaic effect are the main contributing factors to the change in refractive index. Moreover, femtosecond pulse induced refractive index change can be by an order of magnitude higher than values reached with longer laser pulses. Femtosecond DLW opens opportunities for precise control of topological charge separation in lithium niobate crystals in volume and in micrometer scale. Various examples as well as strategies to control and manipulate refractive index change is presented and discussed.

  13. 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

  14. Holographic injection locking of a broad area laser diode via a photorefractive thin-film device.

    PubMed

    van Voorst, P D; de Wit, M R; Offerhaus, H L; Tay, S; Thomas, J; Peyghambarian, N; Boller, K-J

    2007-12-24

    We demonstrate locking of a high power broad area laser diode to a single frequency using holographic feedback from a photorefractive polymer thin-film device for the first time. A four-wave mixing setup is used to generate feedback for the broad area diode at the wavelength of the single frequency source (Ti:Sapphire laser) while the spatial distribution adapts to the preferred profile of the broad area diode. The result is an injection-locked broad area diode emitting with a linewidth comparable to the Ti:Sapphire laser.

  15. 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.

  16. 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.

  17. Oral Gabapentin for Photorefractive Keratectomy Pain

    DTIC Science & Technology

    2011-02-01

    uncorrected and corrected distance visual acuity, corneal topography , intraocular pressure, corneal thickness, cycloplegic refraction, and posterior...alternative for the correction of low to moder- ate myopia or hyperopia. This is especially true for eyes that have reduced central corneal thickness or...postoperative corneal haze are considered drawbacks to PRK compared with LASIK,4,5 the primary disadvantage of PRK is postoperative pain. Topical and oral

  18. 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.

  19. Photorefractive effect in ferroelectric liquid crystals

    NASA Astrophysics Data System (ADS)

    Sasaki, Takeo; Naka, Yumiko

    2014-03-01

    In this paper, we review recent progress of research on the photorefractive effect of ferroelectric liquid crystals. The photorefractive effect is a phenomenon that forms a dynamic hologram in a material. The interference of two laser beams in a photorefractive material establishes a refractive index grating. This phenomenon is applicable to a wide range of devices related to diffraction optics including 3D displays, optical amplification, optical tomography, novelty filters, and phase conjugate wave generators. Ferroelectric liquid crystals are considered as a candidate for practical photorefractive materials. A refractive index grating formation time of 8-10 ms and a large gain coefficient are easily obtained in photorefractive ferroelectric liquid crystals.

  20. Practical correction of a phase-aberrated laser beam using a triphenyldiamine-based photorefractive composite

    NASA Astrophysics Data System (ADS)

    Liang, Yichen; Winiarz, Jeffrey G.

    2017-03-01

    A photorefractive composite based on a triphenyldiamine (TPD) derivative was used to restore a severely phase-aberrated laser beam to a nearly aberration-free state. Here, a forward degenerate four-wave mixing geometry was employed for the elimination of phase distortions and its practical applicability in the transmission of optically encoded data is demonstrated. In addition, it is demonstrated that the experimental geometry is able to effectively restore dynamically updating images. Conventional two-beam coupling and degenerate four-wave mixing experiments were used to characterize the composite subject to the current experimental setup. The two-beam coupling net gain coefficient was 100 cm-1 with an applied external electric field of 70 V/µm. Internal and external diffraction efficiencies of 10 and 6%, respectively, were observed with a similar external electric field. Due to its superior charge-carrier mobility, the TPD-based composite exhibited a response time of 0.28 s, approximately five times faster than traditional PVK-based composites.

  1. 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.

  2. Photorefractive Integrators and Correlators

    DTIC Science & Technology

    1992-12-01

    The use of photorefractive crystals as optically addressed time integrating spatial light modulators in acousto - optic signal processing applications...adaptive acousto - optic processor. These results demonstrated the feasibility of using photorefractives for such applications.... Photorefractive, Acousto - optic processor.

  3. Effects of Altitude Exposure in Photorefractive Keratectomy (PRK) Subjects

    DTIC Science & Technology

    2006-08-01

    Corneal topography data was acquired with EyeSys Vista™ HANDHELD CORNEAL TOPOGRAPHER (Figure 5). The topography unit had the following features...0.10 Diopters (D) Reproducibility: +0.20 D Figure 5: EyeSys Vista™ HANDHELD CORNEAL TOPOGRAPHER Two corneal topography measures of...each eye were accomplished approximately within 30 seconds of each other at each data interval. The corneal topography data was captured and then

  4. Laser fabrication of photorefractive Bragg reflectors, asymmetric waveguides and void arrays in glass

    NASA Astrophysics Data System (ADS)

    Itoh, Kazuyoshi; Watanabe, Wataru; Li, Yan; Yamada, Kazuhiro; Nishii, Junji

    2002-11-01

    We have been studying the refractive index changes and vacancies that are induced in silica glass by the irradiation of ultrashort laser pulses. By scanning the laser beam in the glass we can form 3-D shape of waveguides, arrays of tiny vacancies, called voids, and long holes with microscopic diameters. In this paper, we report on the asymmetry of the waveguide formed by linearly polarized ultrashort pulses. The formation of the photo-induced waveguide is normally accompanied by the filamentation, the self-trapping of laser beam due to nonlinear optical effects. The asymmetric cross-section of the waveguide structures explains properly the illusory birefringence of photo-induced waveguides observed earlier. The cross-sectional forms of the waveguides were observed by polishing and etching the cross-psections. We also report the possibility of forming asymmetric shapes of voids. The asymmetry of voids results from the beam profile. We controlled the profile by inserting apertures before the focusing lens. The asymmetry leads to the polarization dependence of diffraction from the array of voids. We also report on the formation of Bragg grating in glass. The Bragg gratings were formed in soda-lime glass. We succeeded in forming a series of three Bragg gratings. The formation of grating inside glass was confirmed by diffraction experiments and chemical etching of polished cross-sections.

  5. Nonlinear effects in photorefractive crystals

    NASA Astrophysics Data System (ADS)

    Erbschloe, Donald R.

    Photorefractive crystals are materials whose index of refraction is altered under illumination by light. These crystals are both photoconductive and electrooptic. When a nonuniform light intensity pattern is present in the material, photocarriers are generated and redistributed, creating space charge electric fields which change the refractive index locally. These crystals are ideal media for real time holography, and applications include wave amplification, image processing, phase conjugation, and laser beam steering for optical interconnects. This thesis investigates many novel aspects of the photorefractive effect. A study of nonreciprocal behavior identifies a new important consideration in the theory of two-wave mixing between counterpropagating beams-namely the presence of a photocurrent, or frequency detuning between the beams results in a spatially varying beam coupling. A numerical treatment of these important cases provides the first systematic theoretical assessment the control of nonreciprocal transmission and phase shift in lithium niobate, a representative photorefractive crystal. A comparison between crystal types suggests candidates for nonreciprocal applications such as an optical diode.

  6. 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…

  7. 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.

  8. 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.

  9. Nonlinear Effects in Photorefractive Crystals.

    NASA Astrophysics Data System (ADS)

    Erbschloe, Donald Ross

    1988-12-01

    Available from UMI in association with The British Library. Requires signed TDF. Photorefractive crystals are materials whose index of refraction is altered under illumination by light. These crystals are both photoconductive and electrooptic. When a nonuniform light intensity pattern is present in the material, photocarriers are generated and redistributed, creating space charge electrical fields which change the refractive index locally. These crystals are ideal media for real-time holography, and applications include wave amplification, image processing, phase conjugation, and laser beam steering for optical interconnects. This thesis investigates many novel aspects of the photorefractive effect. A study of nonreciprocal behaviour identifies a new important consideration in the theory of two-wave mixing between counterpropagating beams--namely the presence of a photocurrent, or frequency detuning between the beams results in a spatially varying beam coupling. A numerical treatment of these important cases provides the first systematic theoretical assessment of the control of nonreciprocal transmission and phase shift in lithium niobate, a representative protorefractive crystal. A comparison between crystal types suggests candidates for nonreciprocal applications such as an optical diode. A study of bismuth silicon oxide, Bi_ {12}SiO_{20} , as the active gain medium in an oscillator reveals a novel feature, the presence of a light intensity threshold. For one crystal sample no oscillation occurred for incident intensities less than 0.8 mW/cm^2. A surprising new result is the appearance of higher diffracted orders in a crystal sample with a small wedge angle (0.036 ^circ) due to wave mixing between an incident beam and its first codirectional multiple reflection. Several applications for this new means of obtaining beam interaction are discussed--including the study of the photorefractive coupling for very large grating spacings, the investigation of transient

  10. Photorefractive effect in ferroelectric liquid crystal blends containing terthiophene photoconductive chiral dopants

    NASA Astrophysics Data System (ADS)

    Sasaki, Takeo; Yoshino, Masanori

    2016-04-01

    Ferroelectric liquid crystalline mixtures composed of a smectic liquid crystal, a photoconductive chiral dopant, and an electron trap reagent exhibit a large photorefractivity with a rapid response. It is expected that the photorefractive FLC blends can be utilized in dynamic amplification of moving optical signals. In the present study, the photorefractive properties of the ferroelectric liquid crystal blends containing different photoconductive chiral dopants were examined. The durability of the photoconductive chiral dopants during laser irradiation was investigated. Tthe effect of the conduction of photogenerated ionic species on the photorefractivity decay was clarified.

  11. Clinical Outcomes of an Optimized Prolate Ablation Procedure for Correcting Residual Refractive Errors Following Laser Surgery

    PubMed Central

    Chung, Byunghoon; Lee, Hun; Choi, Bong Joon; Seo, Kyung Ryul; Kim, Eung Kwon; Kim, Dae Yune

    2017-01-01

    Purpose The purpose of this study was to investigate the clinical efficacy of an optimized prolate ablation procedure for correcting residual refractive errors following laser surgery. Methods We analyzed 24 eyes of 15 patients who underwent an optimized prolate ablation procedure for the correction of residual refractive errors following laser in situ keratomileusis, laser-assisted subepithelial keratectomy, or photorefractive keratectomy surgeries. Preoperative ophthalmic examinations were performed, and uncorrected distance visual acuity, corrected distance visual acuity, manifest refraction values (sphere, cylinder, and spherical equivalent), point spread function, modulation transfer function, corneal asphericity (Q value), ocular aberrations, and corneal haze measurements were obtained postoperatively at 1, 3, and 6 months. Results Uncorrected distance visual acuity improved and refractive errors decreased significantly at 1, 3, and 6 months postoperatively. Total coma aberration increased at 3 and 6 months postoperatively, while changes in all other aberrations were not statistically significant. Similarly, no significant changes in point spread function were detected, but modulation transfer function increased significantly at the postoperative time points measured. Conclusions The optimized prolate ablation procedure was effective in terms of improving visual acuity and objective visual performance for the correction of persistent refractive errors following laser surgery. PMID:28243019

  12. Ocular drug permeation following experimental excimer laser treatment on the isolated pig eye.

    PubMed

    Scholz, Martina; Schründer, Stephan; Gärtner, Sven; Keipert, Sigrid; Hartmann, Christian; Pleyer, Uwe

    2002-04-01

    Excimer laser photorefractive keratectomy (PRK) is a well-established procedure which is frequently applied to correct myopia. Since structural alterations of the corneal epithelium occur after the treatment, a different drug permeation can be assumed. To investigate the effects of PRK on drug permeation, excimer laser ablations with varying depths were performed on isolated pig eyes. The permeation of lipophilic (diclofenac-sodium; D-Na) and hydrophilic (pilocarpine-hydrochloride; P-HCl model drugs were studied in vitro. Under these experimental conditions, P-HCl demonstrated a significant (p < 0.05) enhancement of permeation in relation to the ablation depth. In contrast, corneal epithelial thickness scarcely influenced the permeation rate of D-Na. Not until removing the entire epithelium did a significantly increased permeability occur, when compared to untreated cornea. These results suggest that PRK may significantly reduce the corneal barrier function and alter pharmacokinetics of topical medication.

  13. Necrotizing Keratitis after Laser Refractive Surgery in Patients with Inactive Inflammatory Bowel Disease

    PubMed Central

    Aman-Ullah, Muhammad; Gimbel, Howard V.; Purba, Mona K.; van Westenbrugge, John A.

    2012-01-01

    Two cases of necrotizing keratitis following laser refractive corneal surgery, with stable and controlled Crohn's disease are described. A 40-year-old woman developed bilateral stromal inflammation and inferior thinning in the right eye along the flap edge within 1 day of uneventful bilateral IntraLase laser-assisted in situ keratomileusis. The other case is a 30-year-old man who also developed bilateral inferior stromal infiltrates 2 days following photorefractive keratectomy. Both cases were aggressively treated with systemic and topical corticosteroids. The infiltrates in both patients gradually resolved, with one relapse during the 7 months period of follow-up in the first case. These cases highlight the importance of taking precautions considering this and similar autoimmune conditions as a relative contraindication to refractive surgery. PMID:22611369

  14. Cross-polarization beam coupling in photorefractive GaAs crystals

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Yeh, Pochi

    1988-01-01

    Theoretical and experimental investigations on the cross-polarization coupling of two contradirectional laser beams in a photorefractive GaAs crystal are reported. There is good agreement between these results.

  15. 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.

  16. Developing photorefractive glass composites

    NASA Astrophysics Data System (ADS)

    Duignan, Jason P.; Taylor, Lesley L.; Cook, Gary

    2002-01-01

    The production of a transparent photorefractive glass composite would offer a useful alternative to bulk crystal materials. We aim to produce such a material by incorporating single domain photorefractive Fe:LiNbO3 particles into a refractive index matched glass host. This glass host is also required to be chemically compatible with the photorefractive material. This compatibility will ensure that the Fe:LiNbO3 particles added to the host glass will remain in the intended crystalline phase and not simply dissolve in the glass. Due to the high refractive index of the Fe:LiNbO3 (no equals 2.35 532 nm), producing a chemically compatible and refractive index matched glass host is technically challenging. By examining common Tellurite, Bismuthate, and Gallate glasses as a starting point and then developing new and hybrid glasses, we have succeeded in producing a chemically compatible glass host and also a refractive index matched glass host. We have produced preliminary glass composite samples which contain a large amount of Fe:LiNbO3. We are currently able to retain nearly 90% of the incorporated Fe:LiNbO3 in the correct crystalline phase, a substantial improvement over previous work conducted in this area in recent years. In this paper we present our progress and findings in this area.

  17. 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

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

    NASA Astrophysics Data System (ADS)

    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.

  19. Stimulated scattering and phase conjugation in photorefractive materials

    NASA Astrophysics Data System (ADS)

    Feinberg, Jack

    1992-01-01

    Applications and properties of nonlinear optical materials were studied, especially photorefractive crystals. A summary includes eight areas of inquiry: (1) demonstration of a new technique for seeing an object buried in or behind a scattering medium using time-resolved holography in a spectral hole-burning material; (2) demonstration of an all-optical switchboard using stimulated, mutually-pumped phase conjugation in a photorefractive crystal; (3) use of optical novelty filters to detect small changes in an optical scene; (4) invention of an electric field correlator to measure the coherence length of picosecond laser pulses, using two-wave mixing in a photorefractive crystal; (5) derivation of a theory of beam coupling and pulse shaping picosecond light pulses in photorefractive crystals; (6) development of a new, multiple level model to explain the nonlinear photoconductivity of barium titanate crystals; (7) investigation of the role of absorption gratings in beam coupling in barium titanate crystals and showing how these gratings can conveniently be used to determine the density of charge in these crystals; and (8) explanation of how stimulated processes cause the curved beam paths observed in mutually-pumped and self-pumped phase conjugators.

  20. 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.

  1. Evaluation of Topical Cyclosporine in Preventing the Development of Corneal Haze after Photorefractive Keratectomy

    DTIC Science & Technology

    2014-05-13

    cataracts , ocular hypertension, and glaucoma. 5,6 Because of the side effect profiles of these two common medications, refractive surgeons have...masked study. Journal of cataract and refractive surgery 2002;28:93-9. 8. Bannale SG, Pundarikaksha HP, Sowbhagya HN. A Prospective, Open-label Study to...after Cataract Extraction. Journal of clinical and diagnostic research : JCDR 2012;6:1499-503. 9. Tempest-Roe S, Joshi L, Dick AD, Taylor SR. Local

  2. Effects of Positive Acceleration on Corneal Stability in Photorefractive Keratectomy (PRK) Subjects

    DTIC Science & Technology

    2005-06-01

    Corneal Topography …………………..………………………………... 17 Visual Acuity…………………………………………………………..... 18 Discussion...Change As A Function of +Gz………………………. 15 Figure 12: Autokeratometry Changes As A Function Of +Gz……………………. 16 Figure 13: Corneal Topography ...both eyes within 10 minutes. Corneal topography data was collected using the EyeSys Vista™ HANDHELD CORNEAL TOPOGRAPHER (HCT) (Figure 8

  3. Photorefractive sol-gel materials

    SciTech Connect

    Chaput, F.; Boilot, J.P.; Gacoin, T.; Darracq, B.; Riehl, D.; Canva, M.; Levy, Y.; Brun, A.

    1996-12-31

    The authors report the synthesis and characterization of photorefractive sol-gel materials that possess covalently attached push-pull azobenzene and carbazole moieties. Molecular structural characterization of the modified silane monomers was achieved by {sup 1}H NMR and infra red spectroscopy. The second-order nonlinear optical properties of the organic-inorganic hybrid films prepared from modified silane monomers were evaluated by second-harmonic generation. The stabilized value of the second harmonic coefficient, d{sub 33}, of films poled by corona discharge, at 1,064 nm fundamental wavelength was found to be 107 pm/V. Photorefractivity was clearly displayed from a two beam coupling experiment.

  4. Excimer laser surface ablation: a review of recent literature.

    PubMed

    O'Brart, David P S

    2014-01-01

    The aim was to review the recently published literature on excimer laser surface ablation procedures, including photorefractive keratectomy (PRK), laser sub-epithelial keratomileusis (LASEK), microkeratome-assisted PRK (epi-LASIK) and trans-epithelial (laser-assisted) PRK, to help elucidate where and how surface ablation may best fit into current refractive surgical practice. The emphasis was on publications within the last three years and included systemic reviews, meta-analyses and randomised controlled trials. Where such evidence did not exist, selective large series cohort studies, case-controlled studies and case series with follow-up preferably greater than six months were examined and included. Refractive and visual outcomes are excellent and comparable to those after LASIK even in complex cases after previous corneal surgery. Indeed, surface ablation combined with corneal collagen cross-linking may be used in selected eyes with biomechanical instability, where LASIK is contraindicated. In addition, there is evidence to suggest that there may be less induction of higher order aberrations with surface techniques. Long-term stability and safety appear to be extremely satisfactory. The literature supports the use of modern excimer laser surface treatments, with outcomes comparable to those after LASIK and evidence of less induction of higher-order aberrations. Follow-up studies at 10 to 20 years indicate excellent stability and safety.

  5. 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

  6. 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.

  7. Stimulated Photorefractive Optical Neural Networks

    DTIC Science & Technology

    1992-12-15

    This final report describes research in optical neural networks performed under DARPA sponsorship at Hughes Aircraft Company during the period 1989...in photorefractive crystals. This approach reduces crosstalk and improves the utilization of the optical input device. Successfully implemented neural ... networks include the Perceptron, Bidirectional Associative Memory, and multi-layer backpropagation networks. Up to 104 neurons, 2xl0(7) weights, and

  8. 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.

  9. 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.

  10. Optical Modulation Via The Photorefractive Effect

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Partovi, A.; Garmire, E.

    1990-01-01

    Rotation of polarization and use of analyzer yield large variations in intensity. Experiments show one beam of light used to change intensity of another beam via photorefractive effect in GaAs. Each beam causes polarization of other beam to rotate. Rotation detected by passing modulated beam through analyzer. Results agree closely with predictions of theory of photorefractive effect. Modulation scheme works with other photorefractive materials of similar crystallographic symmetry.

  11. 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.

  12. Ultrasonic Imaging of Subsurface Objects Using Photorefractive Dynamic Holography

    SciTech Connect

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

    2001-07-01

    The INEEL has developed a photorefractive ultrasonic imaging technology that records both phase and amplitude of ultrasonic waves on the surface of solids. Phase locked dynamic holography provides full field images of these waves scattered from subsurface defects in solids, and these data are compared with theoretical predictions. Laser light reflected by a vibrating surface is imaged into a photorefractive material where it is mixed in a heterodyne technique with a reference wave. This demodulates the data and provides an image of the ultrasonic waves in either 2 wave or 4 wave mixing mode. These data images are recorded at video frame rates and show phase locked traveling or resonant acoustic waves. This technique can be used over a broad range of ultrasonic frequencies. Acoustic frequencies from 2 kHz to 10 MHz have been imaged, and a point measuring (non-imaging) version of the system has measured picometer amplitudes at 1 GHz.

  13. 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.

  14. Photorefractive polymer composites fabricated by injection molding

    NASA Astrophysics Data System (ADS)

    Herlocker, J. A.; Fuentes-Hernandez, C.; Wang, J. F.; Peyghambarian, N.; Kippelen, B.; Zhang, Q.; Marder, S. R.

    2002-02-01

    We report on the fabrication of bulk samples of photorefractive polymers using the injection molding technique. The photorefractive properties of these materials are evaluated by four-wave mixing and two-beam coupling experiments. Samples with good optical quality, high diffraction efficiency, and net optical gain are obtained.

  15. Optical processing using photorefractive GaAs and InP

    NASA Technical Reports Server (NTRS)

    Liu, Duncan T. H.; Cheng, Li-Jen; Luke, Keung L.

    1991-01-01

    The unique features of photorefractive compound semiconductors are presented. The advantages of this class of nonlinear optical materials for optical processing are illustrated with examples using GaAs and InP. The difference between GaAs and InP in the laser power density requirement is discussed.

  16. 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.

  17. 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

  18. Phototherapeutic keratectomy for epithelial basement membrane dystrophy

    PubMed Central

    Lee, Wen-Shin; Lam, Carson K; Manche, Edward E

    2017-01-01

    Purpose The purpose of this study was to evaluate the long-term efficacy of phototherapeutic keratectomy (PTK) in treating epithelial basement membrane dystrophy (EBMD). Methods Preoperative and postoperative records were reviewed for 58 eyes of 51 patients with >3 months follow-up (range 3–170 months) treated for EBMD with PTK after failure of conservative medical treatment at Byers Eye Institute of Stanford University. Symptoms, clinical findings, and corrected distance visual acuity (CDVA) were assessed. The primary outcome measure was symptomatic recurrence as measured by erosions or visual complaints >3 months after successful PTK. Results For eyes with visual disturbances (n=30), preoperative CDVA waŝ20/32 (0.24 Log-MAR, SD 0.21) and postoperative CDVA was ~20/25 (0.07 LogMAR, SD 0.12; P<0.0001). Twenty-six eyes (86.7%) responded to treatment, with symptomatic recurrence in 6 eyes (23.1%) at an average of 37.7 months (SD 42.8). For eyes with painful erosions (n=29), preoperative CDVA was ~20/25 (0.12, SD 0.19) and postoperative CDVA was ~20/20 (0.05. SD 0.16; P=0.0785). Twenty-three eyes (79.3%) responded to treatment, with symptomatic recurrence in 3 eyes (13.0%) at an average of 9.7 months (SD 1.5). The probability of being recurrence free after a successful treatment for visual disturbances and erosions at 5 years postoperatively was estimated at 83.0% (95% confidence interval 68.7%–97.0%) and 88.0% (95% confidence interval 65.3%–96.6%), respectively. Conclusion The majority of visual disturbances and painful erosions associated with EBMD respond to PTK. For those with a treatment response, symptomatic relief is maintained over long-term follow-up. PMID:28031698

  19. Improved Interferometric Photorefractive Optical Processor

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Liu, Tsuen-Hsi

    1991-01-01

    Processing speed increased substantially. Improved optical interferometric image-processing scheme based on four-wave mixing via photorefractive effect in GaAs or InP. Gives rise to index-of-refraction gratings acting as phase-conjugate mirrors: interactions among four input beams generate wave-front-reversed replicas of two of these beams. Each phase-conjugate beam travels precisely back along path of corresponding input beam, regardless of angle of incidence. Any distortions introduced into input beam during forward propagation removed from phase-conjugate beam during backward propagation.

  20. Optical Processing With Photorefractive Semiconductors

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Gheen, Gregory

    1989-01-01

    Experimental phase-conjugate four-wave-mixing apparatus used to demonstrate capabilities of GaAs (and potentially of other photorefractive semiconductors like InP and CdTe) for optical processing of information. With modifications, performs any of three basic image-processing functions: transfer to different light beam, enhancement of edges, and autocorrelation. Includes crystal of GaAs of 5 by 9 by 9 mm with cubic crystalline axes. Advantages include high speed and compatibilty with other semiconductor devices.

  1. Novelty filtered optical correlator using photorefractive crystal

    NASA Technical Reports Server (NTRS)

    Liu, Duncan T. H.; Chao, Tien-Hsin; Cheng, Li-Jen

    1992-01-01

    We demonstrate a new optical correlator in which the correlation peak intensity is increased when the matched input object is moving. The basic configuration of the correlator is the same as a VanderLugt optical correlator consisting of a photorefractive crystal. The principal of this new correlator is based on the dynamic grating erasure property of photorefractive materials. The detail of this principle is described.

  2. Photorefractive Polymers for Updateable 3D Displays

    DTIC Science & Technology

    2010-02-24

    Final Performance Report 3. DATES COVERED (From - To) 01-01-2007 to 11-30-2009 4. TITLE AND SUBTITLE Photorefractive Polymers for Updateable 3D ...ABSTRACT During the tenure of this project a large area updateable 3D color display has been developed for the first time using a new co-polymer...photorefractive polymers have been demonstrated. Moreover, a 6 inch × 6 inch sample was fabricated demonstrating the feasibility of making large area 3D

  3. 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.

  4. Mechanisms for the reciprocity failure in photorefractive polymers

    NASA Astrophysics Data System (ADS)

    Blanche, Pierre-Alexandre; Lynn, Brittany; Norwood, Robert A.; Peyghambarian, Nasser

    2016-09-01

    We measured the diffraction efficiency response of two photorefractive polymer devices according to the duration of the single laser pulse used to record the hologram. The pulse duration was varied from 6 nanoseconds to 1 second, while the pulse energy density was maintained constant at 30 mJ/cm2. This changed the peak power from 5 ×109 mW to 30 mW. We observed a strong reciprocity failure of the efficiency according to the pulse duration, with a reduction as large as a factor 35 between 1 second and 30 μs pulse duration. At even lower pulse duration (< 30 μs), the efficiency leveled out and remained constant down to the nanosecond exposure time. The same behavior was observed for samples composed of the same material but with and without buffer layers deposited on the electrodes, and different voltages applied during the holographic recording. We explained these experimental results based on the charge transport mechanism involved in the photorefractive process. The plateau is attributed to the single excitation of the charge carriers by short pulses (τp < 30 μs). The increase of efficiency for longer pulse duration (τp > 30 μs) is explained by multiple excitations of the charge carriers that allows longer distance to be traveled from the excitation sites. This longer separation distance between the carriers increases the amplitude of the space-charge field, and improves the index modulation. The understanding of the response of the diffraction efficiency according to the pulse duration is particularly important for the optimization of photorefractive materials to be used at high refresh rate such as in videorate 3D display.

  5. Multiple grating formation in photorefractive polymers with azo-dye chromophores

    NASA Astrophysics Data System (ADS)

    Smith, Mark A.; King, Nick R.; Mitchell, Geoffrey R.; O'Leary, Sean V.

    1996-10-01

    Photorefractive polymers which incorporate azo-dyes as the nonlinear chromophore element, can be used not only for generating gratings by the photorefractive effect, but also by photoisomerization of the azo-dye. In the latter mechanism, repeated trans-cis isomerization causes the chromophore molecules to become aligned at right angles to the laser polarization direction, thereby making the material birefringent. These two phenomena are to a large degree independent, and can be studied separately, by appropriate choice of polarization direction of the interacting beams. Furthermore, the diffraction efficiency of the photorefractive gratings is a very sensitive function of the poling field strength, while that of the photoisomerization gratings is less so. In this work, we investigate the components diffracted from each of these gratings formed in a hybrid photorefractive polymer material PVK:TNF:DEACST:disperse red 1. We then explore the possibility of performing some simple optical processing applications, exploiting the flexibility provided by this multiple grating process. A scheme for producing a novelty filter, which displays only the moving parts of a scene is considered. The limitations of these films for such processing applications are discussed.

  6. 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.

  7. Noise in chi (3) and photorefractive amplifiers

    NASA Astrophysics Data System (ADS)

    Sternklar, Shmuel; Glick, Yaakov

    1995-12-01

    A comparison of the noise characteristics of chi (3) and photorefractive coherent amplifiers reveals basic differences in their dependence on operating parameters. Unlike all types of chi (3) amplifiers, which are shown to have a well-defined optimum working point in the region of the self-stimulated scattering threshold, the photorefractive amplifier can be made increasingly quieter by lowering the pump power. This is demonstrated by use of highly doped Co:BaTiO3 in a tight-focus reflection grating geometry. It is shown that scattering from inhomogeneities in the crystal is the major limiting noise source and is significantly higher than predictions resulting from fundamental considerations such as random space-charge noise. An extremely high small-signal gain of 107 was measured with this crystal and geometry. To our knowledge this is the highest photorefractive gain reported to date.

  8. Development of New Photorefractive Polymer Materials

    DTIC Science & Technology

    2015-05-19

    AFRL-OSR-VA-TR-2015-0120 DEVELOPMENT OF NEW PHOTOREFRACTIVE POLYMER MATERIALS Nasser Peyghambarian ARIZONA UNIV BOARD OF REGENTS TUCSON Final Report...ABOVE ORGANIZATION . 1. REPORT DATE (DD-MM-YYYY) 08-05-2015 2. REPORT TYPE Final Performance Report 3. DATES COVERED (From - To) 01-05-2010 - 30-04...2015 4. TITLE AND SUBTITLE Development of New Photorefractive Polymer Materials 5a. CONTRACT NUMBER FA9550-10-1-0207 5b. GRANT NUMBER FA9550-10

  9. 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

  10. Photorefraction of eyes: history and future prospects.

    PubMed

    Howland, Howard C

    2009-06-01

    A brief history of photorefraction, i.e., the refraction of eyes by photography or computer image capture, is given. The method of photorefraction originated from an optical scheme for secret communication across the Berlin wall. This scheme used a lens whose focus about infinity was modulated by a movable reflecting surface. From this device, it was recognized that the vertebrate eye was such a reflector and that its double-pass pointspread could be used to compute its degree of defocus. Subsequently, a second, totally independent invention, more accurately termed "photoretinoscopy," used an eccentric light source and obtained retinoscopic-like images of the reflex in the pupil of the subject's eyes. Photoretinoscopy has become the preferred method of photorefraction and has been instantiated in a wide variety of devices used in vision screening and research. This has been greatly helped by the parallel development of computer and digital camera technology. It seems likely that photorefractive methods will continue to be refined and may eventually become ubiquitous in clinical practice.

  11. Nonlinear photovoltaic effect in Sillenite photorefractive crystals

    NASA Astrophysics Data System (ADS)

    de Oliveira, Ivan; Capovilla, Danilo Augusto; Moura, André L.; Timóteo, Varese S.; Carvalho, Jesiel F.; Frejlich, Jaime

    2017-04-01

    We report on the presence of photovoltaic effect in some Sillenite photorefractive crystals and compare their behavior with that of the well known photovoltaic LiNbO3:Fe crystal. Nonlinear photovoltaic behavior of these Sillenites are also reported here for the first time and explained by the presence of shallow along with deep photovoltaic centers.

  12. GaAs-based photorefractive time-integrating correlator

    NASA Technical Reports Server (NTRS)

    Liu, Duncan T. H.; Luke, Keung L.; Cheng, Li-Jen

    1992-01-01

    A potential application of the photorefractive time-integrating correlator is the real-time radar jamming interference rejection system, using the adaptive filter method; a fast photorefractive crystal is needed for adapting a rapidly changing jamming signal. An effort is presently made to demonstrate and characterize a GaAs-based photorefractive time-integrating correlator, since GaAs crystals are 2-3 orders of magnitude faster than most other alternatives.

  13. 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.

  14. Properties and applications of photorefractive GaAs

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Liu, Duncan T. H.

    1990-01-01

    Photorefractive semiconductors have the attractive features of fast response times and operation at near-infrared wavelengths. This has opened some new research opportunities in the field of photorefractive nonlinear optics which is significant for applications in real-time image processing and optical computing. This paper presents recent experimental demonstrations of several basic optical information processing techniques using photorefractive GaAs crystals. The results of these demonstrations illustrate that photorefractive compound semiconductors has a great potential as a new medium for light beam interaction based on the dynamic holographic principle.

  15. The Progression of Haze Formation in Rabbit Corneas Following Phototherapeutic Keratectomy

    PubMed Central

    Gibson, Daniel J.; Tuli, Sonal S.; Schultz, Gregory S.

    2013-01-01

    Purpose. To determine the topographical location and time course of development of corneal haze in a phototherapeutic keratectomy model using slit lamp examination, macrophotography, quantitative image analysis, and immunofluorescence staining of corneal sections. Methods. Rabbit corneas were ablated with an excimer laser and were observed and graded for haze via slit lamp, imaged, and graded by macrophotography. Corneal sections were stained for α-smooth muscle actin (α-SMA) and tenascin-C (TNC). The distribution of haze imaged in the macrophotographs and density of α-SMA and TNC staining were compared. A daily image time course of haze formation was generated using macrophotography. Results. The first signs of corneal haze were apparent shortly after reepithelialization. The haze was distributed as a ring at the wound margin in all cases, while nearly all corneas also had some central islands of haze initiation. With time, the haze spread within the ablated zone and intensified. The pattern of immunofluorescent staining for α-SMA and TNC at the wound margin mirrored the haze distribution, spread, and intensification with time. Conclusions. The initiation and spread of subepithelial haze begins shortly after reepithelialization. The haze then spreads from the loci of initiation and becomes more dense with time, maturing as early as 14 days after wounding. The improved temporal and spatial resolution provided by these data improve the current model of light-scattering haze formation in wounded corneas, which will improve the design of studies aimed at maintaining corneal clarity following acute injury or surgery. PMID:23800768

  16. Analytical solution for photorefractive screening solitons

    NASA Astrophysics Data System (ADS)

    Królikowski, Wieslaw; Luther-Davies, Barry; McCarthy, Glen; Bledowski, Aleksander

    2000-02-01

    We study formation and interaction of one-dimensional screening solitons in a photorefractive medium with sublinear dependence of the photoconductivity on light intensity. We find an exact analytical solution to the corresponding nonlinear Schrödinger equation. We show that these solitons are stable in propagation and their interaction is generic for solitons of saturable nonlinearity. In particular, they may fuse or ``give birth'' to new solitons upon collision.

  17. 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.

  18. [Epi-Bowman Keratectomy: Clinical Evaluation of a New Method of Surface Ablation].

    PubMed

    Taneri, S; Kießler, S; Rost, A; Schultz, T; Elling, M; Dick, B

    2017-02-10

    Purpose A new device for epithelial abrasion before excimer laser surface ablation or corneal cross-linking (CXL) has recently been introduced (Epi-Clear™, Orca Surgical, Kiryat-Shmona, Israel). We have reviewed the literature on the clinical results, potential benefits and drawbacks of this instrument, compared to other methods of epithelial removal. Method Literature search for "Epi-Bowman Keratectomy", "Epi-clear", and "Epikeratome" yielded 1 peer-review publication, 1 non-peer-review publication, 18 posters and presentations at international conferences (European Society of Cataract and Refractive Surgeons [ESCRS] and American Society of Cataract and Refractive Surgery [ASCRS]) on the use of the Epi-Clear™ device before surface ablation, 2 posters on the use of Epi-Clear before corneal crosslinking and 1 presentation on the experimental use of Epi-Clear for removal of a pterygium. Results Comparison of laser ablation after epithelial removal with the Epi-Clear device (Epi-Bowman Keratectomy™, EBK™) to other established methods of surface ablation, i.e. alcohol-assisted PRK or PRK with a metallic scraper, EBK, suggests that the results are generally similar. Pain perception, haze formation, and epithelial healing are reported to be better than with conventional surface ablation methods. Studies evaluating the use of the Epi-Clear device before CXL report that the healing time is significantly reduced and that less pain is perceived. Conclusion The Epi-Clear device seems to be a promising new option for epithelial removal before refractive laser ablation, although a convincing explanation for its potential superiority is still missing. In contrast, when the Epi-Clear device is used before CXL, then the Bowman's layer remains intact; this may provide an adequate explanation for the reported benefits of this application. However, currently available studies are of low level of evidence, so that more prospective randomised trials are needed for a robust

  19. Two-Photon Optical Storage in Photorefractive Polymers in the Near-Infrared Spectral Range

    NASA Astrophysics Data System (ADS)

    Day, Daniel; Gu, Min; Smallridge, Andrew

    We report the use of a polymer-based photorefractive material for three-dimensional bit optical data storage using near-infrared illumination. The research was conducted using photorefractive materials that were fabricated in two polymer matrices: poly(N-vinylcarbazole) (PVK) and poly(Methyl Methacrylate) (PMMA). The recording samples also consisted of the following compounds in various proportions: 2,5-dimethyl-4-(p-nitrophenylazo)anisole (DMNPAA), 2,4,7-trinitro-9-fluorenone (TNF) and N-ethylcarbazole (ECZ). Two-photon excitation was used as the recording mechanism to achieve rewritable bit data storage in a photorefractive polymer. As a result of two-photon excitation, the quadratic dependence of the excitation on the incident intensity produces an excitation volume that is confined to the focal region in both the transverse and axial directions. The use of ultrashort pulsed lasers, while effective, is not a practical solution for an optical data storage system. This research demonstrates the ability to produce three-dimensional rewritable bit data storage using continuous-wave illumination. Using this technology it has been possible to achieve a density of 88 Gbits/cm3, which in the future could be increased to 3.5 Tbits/cm3.

  20. Optical correlators with fast updating speed using photorefractive semiconductor materials

    NASA Technical Reports Server (NTRS)

    Gheen, Gregory; Cheng, Li-Jen

    1988-01-01

    The performance of an updatable optical correlator which uses a photorefractive semiconductor to generate real-time matched filters is discussed. The application of compound semiconductors makes possible high-speed operation and low optical input intensities. The Bragg diffraction is considered, along with the speed and power characteristics of these materials. Experimental results on photorefractive GaAs are presented.

  1. Applicability of the band transport (Kukhtarev) model to photorefractive polymers

    NASA Astrophysics Data System (ADS)

    Ducharme, Stephen

    1995-08-01

    The band transport model of space-charge production has proved very successful in describing photorefractive phenomena in a wide range of inorganic crystals, ranging from high-mobility semiconductors like GaAs, to highly insulating ferroelectrics like BaTiO3. This success is primarily due to the applicability of a generic picture of charge transport in extrinsic crystalline semiconductors, a picture that becomes cloudy in noncrystalline systems like the new photorefractive polymers. Photorefractive polymers exhibit the classic photorefractive behaviors such as photoconduction, electro-optic response, hologram formation and storage, and two-beam energy coupling, all without benefit of a crystalline lattice or well defined conduction band. In this report, I will outline how the band transport model can be adapted to describe photorefraction in noncrystalline materials by the dual expediencies of renaming certain embarrassing 'constants' and admitting that they are strongly dependent on the total electric field.

  2. Visual outcomes of topography-guided excimer laser surgery for treatment of patients with irregular astigmatism.

    PubMed

    Ghoreishi, Mohammad; Naderi Beni, Afsaneh; Naderi Beni, Zahra

    2014-01-01

    The aim of this study was to evaluate the efficacy, safety, and predictability of topography-guided treatments to enhance refractive status following other corneal surgical procedures. In a prospective case series study, 28 consecutive eyes of 26 patients with irregular astigmatism after radial keratotomy, corneal transplant, small hyperopic and myopic excimer laser optical zones, and corneal scars were operated. Laser-assisted in situ keratomileusis (LASIK) (n = 8) and photorefractive keratectomy (PRK) (n = 20) were performed using the ALLEGRETTO WAVE excimer laser and topography-guided customized ablation treatment software. Preoperative and postoperative uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), manifest and cycloplegic refraction, and corneal topography with asphericity were analyzed in 12 months follow-up. Uncorrected visual acuity (UCVA) changed from 0.2 ± 0.2 or (20/100 ± 20/100) to 0.51 ± 0.31 or (20/40 ± 20/60) in the LASIK group (P = 0.01) and from 0.34 ± 0.16 or (20/60 ± 20/120) to 0.5 ± 0.23 or (20/40 ± 20/80) in the PRK group (P = 0.01). Refractive cylinder decreased from -3.2 ± 0.84 diopters (D) to -2.06 ± 0.42 D in the LASIK group (P = 0.07) and from -2.25 ± 0.39 D to -1.5 ± 0.23 D in the PRK group (P = 0.008). Best corrected visual acuity did not change significantly in either group. Topography-guided treatment is effective in correcting the irregular astigmatism after refractive surgery. Topography-guided PRK can significantly reduce irregular astigmatism and increase the UCVA and BCVA.

  3. True-Time-Delay Adaptive Array Processing Using Photorefractive Crystals

    NASA Astrophysics Data System (ADS)

    Kriehn, G. R.; Wagner, K.

    Radio frequency (RF) signal processing has proven to be a fertile application area when using photorefractive-based, optical processing techniques. This is due to a photorefractive material's capability to record gratings and diffract off these gratings with optically modulated beams that contain a wide RF bandwidth, and include applications such as the bias-free time-integrating correlator [1], adaptive signal processing, and jammer excision, [2, 3, 4]. Photorefractive processing of signals from RF antenna arrays is especially appropriate because of the massive parallelism that is readily achievable in a photorefractive crystal (in which many resolvable beams can be incident on a single crystal simultaneously—each coming from an optical modulator driven by a separate RF antenna element), and because a number of approaches for adaptive array processing using photorefractive crystals have been successfully investigated [5, 6]. In these types of applications, the adaptive weight coefficients are represented by the amplitude and phase of the holographic gratings, and many millions of such adaptive weights can be multiplexed within the volume of a photorefractive crystal. RF modulated optical signals from each array element are diffracted from the adaptively recorded photorefractive gratings (which can be multiplexed either angularly or spatially), and are then coherently combined with the appropriate amplitude weights and phase shifts to effectively steer the angular receptivity pattern of the antenna array toward the desired arriving signal. Likewise, the antenna nulls can also be rotated toward unwanted narrowband jammers for extinction, thereby optimizing the signal-to-interference-plus-noise ratio.

  4. Photorefractive processing for large adaptive phased arrays

    NASA Astrophysics Data System (ADS)

    Weverka, Robert T.; Wagner, Kelvin; Sarto, Anthony

    1996-03-01

    An adaptive null-steering phased-array optical processor that utilizes a photorefractive crystal to time integrate the adaptive weights and null out correlated jammers is described. This is a beam-steering processor in which the temporal waveform of the desired signal is known but the look direction is not. The processor computes the angle(s) of arrival of the desired signal and steers the array to look in that direction while rotating the nulls of the antenna pattern toward any narrow-band jammers that may be present. We have experimentally demonstrated a simplified version of this adaptive phased-array-radar processor that nulls out the narrow-band jammers by using feedback-correlation detection. In this processor it is assumed that we know a priori only that the signal is broadband and the jammers are narrow band. These are examples of a class of optical processors that use the angular selectivity of volume holograms to form the nulls and look directions in an adaptive phased-array-radar pattern and thereby to harness the computational abilities of three-dimensional parallelism in the volume of photorefractive crystals. The development of this processing in volume holographic system has led to a new algorithm for phased-array-radar processing that uses fewer tapped-delay lines than does the classic time-domain beam former. The optical implementation of the new algorithm has the further advantage of utilization of a single photorefractive crystal to implement as many as a million adaptive weights, allowing the radar system to scale to large size with no increase in processing hardware.

  5. 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.

  6. Development of photorefractive polymers for real-time optical information storage

    NASA Astrophysics Data System (ADS)

    Mangaiyarkarasi, D.; Palanisamy, P. K.; Kannan, P.

    1999-03-01

    A large number of strong nonlinear optical and electro optical molecules and crystals are identified recently. With the discovery of the photorefractive (PR) effect and early realization of its potential utility, PR materials are of considerable interest for the development of all optical devices, such as high density optical data storage and image processing techniques. Organic materials are known to show strong electro optic effects. In organic materials, the properties required for the PR effect including photosensitivity, photoconductivity and electro optic response are provided by different molecules. As a result, the properties can be optimized separately, unlike in inorganic PR crystals such as LiNbO3. This paper describes the utilization of third order non-linearity induced in Xanthene dye doped gelatin and poly (eosin acrylate) & poly (eosin acrylate-co-isobutyl acrylate) films resulting in direct storage without the need for any further processing i.e., no wet chemical or post thermal/photochemical processing are required. With required amount of solvent and monomer in the presence of benzoyl peroxide (initiator), polymerization reaction was carried out under nitrogen atmosphere. Polymer samples were characterized by NMR, IR, FT-IR & TGA. The polymers were soluble in THF, DMSO, DMF & DMAC solvents and form good optical quality films by spin as well as dip coating. Polymer thin films were prepared with different concentrations of polymer solution onto the glass slides. The UV-visible absorption spectra of the spin coated polymer films showed a maximum at 538 nm. In our simplest optical system, Q- switched, second harmonic Nd-YAG laser light at wavelength 532 nm was used for recording. Two beams split from the same laser were made to superpose with path difference less than the coherent length. One of the beam acted as information carrying beam while the other acted as reference beam. In this present study, we report the direction formation of surface

  7. New Meta and Nanomaterials for Photorefractive Enhancement and Photorefractive Two-Beam Coupling

    DTIC Science & Technology

    2010-03-12

    Centro de Investigacion de Quimica Aplicada Blvd. Enrique reyna, No. 140 Saltillo, Coahuila, Mexico 25253 AFOSR FA9550-09-1-0023 12 March 2010...ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NUMBER CENTRO DE INVESTIGACION EN QUIMICA APLICADA BLVD ENRIQUE REYNA NO 140 SALTILLO 25253...Photorefractive Two-Beam Coupling Ronald F. Ziolo Centro de Investigacion de Quimica Aplicada Saltillo, Coahuila, Mexico 25253 Grant

  8. Low-noise preamplifier for multistage photorefractive image amplification

    NASA Astrophysics Data System (ADS)

    Breugnot, S.; Rajbenbach, H.; Defour, M.; Huignard, J.-P.

    1995-07-01

    We present a two-beam coupling configuration in photorefractive BaTiO3 that provides a low-noise amplification of the signal to be detected. A two-wave mixing gain of 100 is reached, in conjunction with very low beam fanning background in the signal direction. The extensions of this configuration to photorefractive heterodyne detection and to multistage image amplification are theoretically and experimentally studied.

  9. Optical image processing by using a photorefractive spatial soliton waveguide

    NASA Astrophysics Data System (ADS)

    Liang, Bao-Lai; Wang, Ying; Zhang, Su-Heng; Guo, Qing-Lin; Wang, Shu-Fang; Fu, Guang-Sheng; Simmonds, Paul J.; Wang, Zhao-Qi

    2017-04-01

    By combining the photorefractive spatial soliton waveguide of a Ce:SBN crystal with a coherent 4-f system we are able to manipulate the spatial frequencies of an input optical image to perform edge-enhancement and direct component enhancement operations. Theoretical analysis of this optical image processor is presented to interpret the experimental observations. This work provides an approach for optical image processing by using photorefractive spatial solitons.

  10. 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

  11. 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.

  12. Spatial Rogue Waves in Photorefractive Ferroelectrics.

    PubMed

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

    2015-08-28

    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.

  13. Enhancement of blue photorefractive properties in Mg:Fe:Cu:SLiNbO3 crystals with near stoichiometry

    NASA Astrophysics Data System (ADS)

    Dai, Li; Jiao, Shanshan; Xu, Chao; Li, Dayong; Lin, Jiaqi; Xu, Yuheng

    2014-02-01

    Using the top seeded solution growth technique, near stoichiometric Mg:Fe:Cu:SLiNbO3 crystals have been grown by using K2O as flux. Infrared transmission spectra were measured and defect structure and change of threshold value were investigated. Using Kr+ laser as light source (blue light with wavelength of 476 nm) the photorefractive properties of crystals were measured. The diffraction efficiency of 76.3%, the short response time of 11 s, the dynamic range of 27.39, the sensitivity of 2.09 cm/J, and the refractive index change of 8.67 × 10-5 were obtained. The blue photorefractive properties were enhanced. As the holes are the dominant charge carriers, the short wavelength blue light which exhibits high energy can excite the holes from both of the shallow and the deep trap centers with the same phase. It was found that the so-called optical damage-resistant dopant such as Mg2+ ions no longer functioned as the damage resistant at 476 nm wavelength, but turned to enhance the blue photorefractive characteristics.

  14. Photorefractive spatial mode converter for multimode-to-single-mode fiber-optic coupling.

    PubMed

    Chiou, A; Yeh, P; Yang, C; Gu, C

    1995-05-15

    We report what is to our knowledge the first experimental demonstration of a photorefractive spatial mode converter (based on mutually pumped phase conjugation) that couples light efficiently from a multimode fiber into a singlemode fiber with an extremely large degree of tolerance to misalignment. Using an argon laser (514.5 nm) and a barium titanate crystal, we have demonstrated that the laser light can be coupled from a multimode fiber (core diameter 100 microm, numerical aperture 0.37) into a single-mode fiber (core diameter 2.9 microm, numerical aperture 0.11), with an efficiency of ~15% and an alignment tolerance of ~100 microm. The coupling efficiency is more than 2 orders of magnitude, and the tolerance to misalignments is more than 30 times better than the corresponding values achievable by conventional techniques.

  15. 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

  16. 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

  17. Autowaves in two-wave mixing in photorefractive media

    SciTech Connect

    Prudkovskii, Pavel A

    2011-01-31

    The phase part of the system of equations describing two-wave mixing in a photorefractive strongly inertial medium is studied analytically and numerically. It is shown that the solution of the system of equations evolves through a series of quasi-stationary states, and the system switches between them due to a nonlinear wave. The velocity and profile of such a 'switching wave' are completely determined by these states, which is an indication of an autowave process. The results show that the development of four-wave mixing in a strongly illuminated photorefractive medium is inevitably accompanied by intensity fluctuations. (nonlinear optical phenomena)

  18. 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.

  19. Zernike Interpretation in Ocular Photorefraction Images

    NASA Astrophysics Data System (ADS)

    Shi, Lei; Chen, Ying-Ling; Baker, Kevin; Lewis, J. W. L.; Tan, Bo; Wang, Ming

    2007-11-01

    Photorefraction (PR) is a common method used in public vision screening for near/far-sightedness and cross eyes. The eye is photographed with an illuminating source close to the camera. Diagnosis is given by the intensity distribution across the pupil reflex. In this study, an enhanced PR system is assembled and used to obtain monocular images from patients in Wang Vision Institute. Thirteen rapidly sequenced IR images are taken for each eye. A target-finding algorithm locates the pupil, and the scaled intensity distribution of the pupil is color-coded into 8 levels. The false-color maps show distinguished patterns between normal and abnormal eyes. Zernike analysis of the image provides quantitative measure of the 1^st, 2^nd, and high-order ocular aberrations. The results reveal that normal eyes are predominantly described by 1st order coefficients, while abnormal eyes exhibit a significant contribution from high-order terms. This study shows that PR can be extended to detect high-order aberration in addition to its traditional applications.

  20. 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.

  1. Matrix.Vector Multiplication In Thin Photorefractive Crystal

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Gheen, Gregory O.

    1990-01-01

    Thin GaAs device integrated with other electronic and optoelectronic devices. Experiments show matrix.vector multiplication performed optically by four-wave mixing in thin crystal of GaAs. Concept applicable to thin crystals of other photorefractive materials having suitable electro-optical properties and same crystalline symmetry as that of GaAs.

  2. Updateable 3D Display Using Large Area Photorefractive Polymer Devices

    DTIC Science & Technology

    2013-04-01

    2011.  C. W. Christenson, et al., " Interdigitated coplanar electrodes for enhanced sensitivity in a photorefractive polymer", Optics Letters, Vol...researcher to tailor the flow of electrons between the electrodes and acts as an insulator to minimize the opportunities for electrical breakdown

  3. Photorefractive digital holographic microscopy applied in microstructures analysis

    NASA Astrophysics Data System (ADS)

    Brito, Isis V.; Gesualdi, Marcos R. R.; Ricardo, Jorge; Palácios, Francisco; Muramatsu, Mikiya; Valin, José L.

    2013-01-01

    In this work, we present a Photorefractive Digital Holographic Microscopy (PRDHM) technique based on the writing-reading holographic process in photorefractive Bi12TiO20 (BTO) crystal and the obtainment of phase and amplitude of the object wave were performed by a digital holographic method. We demonstrate that the wave diffracted by a photorefractive hologram recorded in a BTO crystal can be combined with a reference wave to record a second hologram in a CCD sensor in a configuration of digital holographic microscopy. The experimental measurements were performed on samples like red blood cells and a thin film structure, and were obtained quantitative values of amplitude and phase of the object wave, as well as 3D graphs, of the analyzed samples by the digital reconstruction holographic method. This technique presents a new method in replacement of the usual methods for reconstruction of holograms recorded in a photorefractive crystal and also presents the possibilities to obtain 3D phase images for surfaces characterization and applications in dynamic holography.

  4. Characterization of highly photorefractive and active silica-germania sputtered thin films

    NASA Astrophysics Data System (ADS)

    Berneschi, S.; Brenci, M.; Chiasera, A.; Ferrari, M.; Nunzi Conti, G.; Pelli, S.; Sebastiani, S.; Tosello, C.; Righini, G. C.

    2006-02-01

    We report on the characterization of highly photorefractive Er 3+/Yb 3+-doped silica-germania planar waveguides deposited by radio-frequency-magnetron-sputtering technique. Details of the deposition process in order to get low loss, single mode waveguides at 1550 nm are described. The material presents an intense absorption band in the UV region and irradiation by a KrF excimer laser source produces large positive refractive index changes, without the need of particular sensitization procedures. Dark line spectroscopy of the waveguide modes at 635 nm was performed to calculate the index change under UV exposure. Highly efficient photo-induced phase gratings have been fabricated in the slab waveguide. Waveguides spectroscopic properties of the 4I 13/2 <=> 4I 15/2 transition of the Er 3+ ion, including lifetime and emission bandwidth, were examined. Photoluminescence excitation spectroscopy was also recorded to detect the Yb 3+ to Er 3+ energy transfer process.

  5. 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.

  6. Effects of photocrosslinking on photorefractive properties in polymer-liquid crystal composites

    NASA Astrophysics Data System (ADS)

    Ono, Hiroshi; Hasebe, Ryoya; Sasaki, Tomoyuki; Noda, Kohei; Kawatsuki, Nobuhiro

    2014-03-01

    This article presents effects of photocrosslinking on photorefractive properties in polymer-liquid crystal composites doped with fullerene (C60) as a photoconductive agent. The efficiency of the photorefraction was improved by crosslinking the polymer network and reached near to the theoretical limit for the thin phase grating. The carrier conduction in the composite films was investigated and the high-performance photorefractivity of the photocrosslinked mesogenic composite was explained by low dark current and high photocurrent. The firm crosslinked polymer network in the polymer-liquid crystal composite has also employed for the stable photorefractive diffraction at elevated temperature and under a static dc field applied the mesogenic composite film.

  7. The U.S. Air Force Photorefractive Keratectomy (PRK) Study: Evaluation of Residual Refractive Error and High- and Low-Contrast Visual Acuity

    DTIC Science & Technology

    2006-07-01

    12-, and 24-Mo Post-PRK Evaluations That Gained or Lost at Least One Line of Letters, Compared to Their Best-Corrected Presurgical Baseline, on the...24-Mo Post-PRK Evaluations That Gained or Lost at Least One Line of Letters, Compared to Their Best-Corrected Presurgical Baseline, on the Bailey...or identify certain targets as compared to their performance when best corrected preoperatively to a possible 20/10 with spectacles or contact

  8. 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.

  9. Cyanoacrylate adhesive with conjunctival resection and superficial keratectomy in Mooren's ulcer.

    PubMed

    Agrawal, V; Kumar, A; Sangwan, V; Rao, G N

    1996-03-01

    Seventeen eyes of thirteen patients with Mooren's ulcer were treated with a combination therapy of local and systemic steroids, conjunctival resection, superficial keratectomy and application of cyanoacrylate tissue adhesive. The pathology was classified as acute, subacute and chronic. Ulcers were graded based on the extent of corneal thinning, degree and extent of ulceration, and amount of inflammation. Fourteen eyes (82.4%) healed completely with formation of a vascularised scars, while three eyes (17.6%) failed to respond to treatment and either went into phthisis bulbi or healed with gross tissue distortion. Our study suggests an early intervention of this therapy with cyanoacrylate tissue adhesive application for effective control of Mooren's ulceration.

  10. 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.

  11. Photorefractive phased array antenna beam-forming processor

    NASA Astrophysics Data System (ADS)

    Sarto, Anthony W.; Wagner, Kelvin H.; Weverka, Robert T.; Blair, Steven M.; Weaver, Samuel P.

    1996-11-01

    A high bandwidth, large degree-of-freedom photorefractive phased-array antenna beam-forming processor which uses 3D dynamic volume holograms in photorefractive crystals to time integrate the adaptive weights to perform beam steering and jammer-cancellation signal-processing tasks is described. The processor calculates the angle-of-arrival of a desired signal of interest and steers the antenna pattern in the direction of this desired signal by forming a dynamic holographic grating proportional to the correlation between the incoming signal of interest from the antenna array and the temporal waveform of the desired signal. Experimental results of main-beam formation and measured array-functions are presented in holographic index grating and the resulting processor output.

  12. 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

    2016-10-01

    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.

  13. 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.

  14. Orientation of optic axis in wedged photorefractive crystals

    NASA Astrophysics Data System (ADS)

    Kos, Konstantine; Siahmakoun, Azad Z.

    1996-02-01

    A holographic method for finding the orientation of the optic axis of uniaxial photorefractive crystals is proposed. A theoretical procedure for determining the wedge angle of such crystals has also been developed. Two BaTiO 3 crystals grown by the same vender are examined and the resulting measurements lead to the values of wedge angle with an accuracy of about ±0.1°.

  15. Infrared predetection dynamic range compression via photorefractive crystals

    NASA Technical Reports Server (NTRS)

    Liu, Hua-Kuang; Cheng, Li-Jen

    1988-01-01

    The theoretical basis and practical implementation of a predetection dynamic-range compression technique for IR sensor systems are discussed. The approach takes advantage of the nonlinear intensity dependence of the gain coefficient in photorefractive crystals. Its feasibility is demonstrated in numerical computations using the experimental data of Cheng and Partovi (1986) on two-wave mixing in GaAs at 1.15 micron wavelength.

  16. 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.

  17. Photorefractivity in a polymeric composite photosensitized with NiS nanocrystals

    NASA Astrophysics Data System (ADS)

    Fears, Tyler M.; Anderson, Charles; Winiarz, Jeffrey G.

    2008-10-01

    The photorefractive performance of a polymeric composite photosensitized through the inclusion of NiS nanocrystals is described. The nanocrystals were characterized using visible-absorption spectroscopy, energy-dispersive x-ray spectroscopy, and transmission electron microscopy. We further demonstrate the ability to enhance various aspects of the composite's photorefractive performance by performing ligand exchange on the nanocrystals prior to their incorporation into the polymer composite. This procedure resulted in a lowering of the overmodulation voltage from ˜70to˜50V/μm without affecting the maximum diffraction efficiency of ˜40%. An increase in the two-beam-coupling gain coefficient was similarly observed, increasing from 38to79cm-1. The photoconductivities were used in determining the overall quantum efficiencies associated with the photorefractive devices. All experiments were conducted at 633nm and the data represent a significant improvement in the photorefractive performance of inorganic-organic hybrid photorefractive materials.

  18. 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

  19. Doppler Frequency-Shift Compensated Photorefractive Interferometer for Ultrasound Detection on Objects in Motion

    NASA Astrophysics Data System (ADS)

    Campagne, B.; Blouin, A.; Néron, C.; Monchalin, J.-P.

    2003-03-01

    Two-wave mixing based interferometry has been demonstrated to be a powerful technique for non-contact, broadband and speckle insensitive measurements of the small surface displacements produced by ultrasonic waves propagating in an object. When the object is in rapid motion along the line-of-sight of the probing laser or when the laser beam is rapidly scanned on a wavy surface, the two-wave mixing photorefractive interferometer loses sensitivity to the point it could become useless. To circumvent the Doppler frequency-shift produced by this relative motion, we propose a dynamic compensation scheme. We report a particularly simple scheme to implement this concept by monitoring the low-frequency output signal of a balanced two-wave mixing demodulator whose output is proportional to the frequency difference between the pump and signal beams, and feeding this signal back to the acousto-optic shifter. With this new concept, the two-wave mixing interferometer can operate on objects in rapid motion while maintaining its sensitivity to low frequency ultrasound.

  20. 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

  1. Laser adaptive holographic hydrophone

    SciTech Connect

    Romashko, R V; Kulchin, Yu N; Bezruk, M N; Ermolaev, S A

    2016-03-31

    A new type of a laser hydrophone based on dynamic holograms, formed in a photorefractive crystal, is proposed and studied. It is shown that the use of dynamic holograms makes it unnecessary to use complex optical schemes and systems for electronic stabilisation of the interferometer operating point. This essentially simplifies the scheme of the laser hydrophone preserving its high sensitivity, which offers the possibility to use it under a strong variation of the environment parameters. The laser adaptive holographic hydrophone implemented at present possesses the sensitivity at a level of 3.3 mV Pa{sup -1} in the frequency range from 1 to 30 kHz. (laser hydrophones)

  2. 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.

  3. 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.

  4. Interdigitated coplanar electrodes for enhanced sensitivity in a photorefractive polymer.

    PubMed

    Christenson, C W; Greenlee, C; Lynn, B; Thomas, J; Blanche, P-A; Voorakaranam, R; Hilaire, P St; LaComb, L J; Norwood, R A; Yamamoto, M; Peyghambarian, N

    2011-09-01

    Organic photorefractive polymer composites can be made to exhibit near 100% diffraction efficiency and fast writing times, though large external slants are needed to project the applied field onto the grating vector. We show here that the use of interdigitated electrodes on a single plane provides similar performance to these standard devices and geometries but without a external slant angle. This new device's structure also greatly improves the diffraction efficiency and sensitivity compared to less slanted standard devices necessary for some real applications, such as holographic displays, optical coherence imaging, and in-plane switching.

  5. 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.

  6. Dynamic holographic interferometry by photorefractive crystals for quantitative deformation measurements.

    PubMed

    Pouet, B; Krishnaswamy, S

    1996-02-10

    A holographic interferometer that uses two-wave mixing in a photorefractive (Bi12SiO20) crystal under an applied ac field is described. The interferometer uses a repetitive sequence of separate record and readout times to obtain quasi real-time holographic interferograms of vibrating objects. It is shown that a good signal-to-noise ratio of the interferometer is obtained by turning off the object illumination and the applied ac field during readout of the hologram. The good signal-to-noise ratio of the resulting holographic interferograms enables phase measurement, which allows for quantitative deformation analysis.

  7. Examination of the restoration of epithelial barrier function following superficial keratectomy.

    PubMed

    Hutcheon, Audrey E K; Sippel, Kimberly C; Zieske, James D

    2007-01-01

    The goal of the present study was to determine the rate of restoration of the corneal epithelial barrier following a superficial keratectomy using a functional assay of tight junction integrity. Adult Sprague-Dawley rats were anesthetized and a 3-mm superficial keratectomy was performed. The eyes were allowed to heal from 4 h to 8 weeks and the rate of epithelial wound closure was determined. To examine the restoration of the barrier function, EZ-Link Sulfo-NHS-LC-Biotin (LC-Biotin) was applied to all eyes, experimental and control, for 15 min at the time of sacrifice. This compound does not penetrate through intact tight junctions. Indirect immunofluorescence was performed with anti-laminin, a marker of basement membrane; fluorescein-conjugated streptavidin to detect the biotinylated marker; and anti-occludin and anti-ZO-1, markers of tight junctions. Epithelial wound closure was observed at 36-42 h after wounding. LC-Biotin did not penetrate the intact epithelium. Upon wounding, LC-Biotin penetrated into the stroma subjacent and slightly peripheral to the wound area. This pattern was present from 4-48 h post-wounding. The area of LC-Biotin localization decreased with time and the functional barrier was restored by 72 h. Occludin and ZO-1 were present at all time points. The number of cell layers expressing these proteins appeared to increase at 48 and 72 h. Continuous laminin localization was not observed until at least 7 days after wounding. Barrier function is restored within 1-1.5 days after epithelial wound closure. The loss of barrier function does not extend beyond the edge of the original wound. The restoration of barrier function does not appear to correlate with reassembly of the basement membrane in this model.

  8. Phase and direction dependence of photorefraction in a low-frequency strong circular-polarized plane wave

    NASA Astrophysics Data System (ADS)

    Huang, Yong-Sheng; Wang, Nai-Yan; Tang, Xiu-Zhang

    2015-05-01

    Contrary to the superposition principle, it is well known that photorefraction exists in the vacuum with the presence of a strong static field, a laser field, or a rotational magnetic field. Different from the classical optical crystals, the refractive index also depends on the phase of the strong electromagnetic field. We obtain the phase and direction dependence of the refractive index of a probe wave incident in the strong field of a circular-polarized plane wave by solving the Maxwell equations corrected by the effective Lagrangian. It may provide a valuable theoretical basis to calculate the polarization evolution of waves in the strong electromagnetic circumstances of pulsar or neutron stars. Project supported by the National Basic Research Program of China (Grant No. 2011CB808104) and the National Natural Science Foundation of China (Grant No. 11105233).

  9. Segregation and inhomogeneities in photorefractive SBN fibers

    NASA Astrophysics Data System (ADS)

    Erdei, Sandor; Galambos, Ludwig; Tanaka, Isao; Hesselink, Lambertus; Ainger, Frank W.; Cross, Leslie E.; Feigelson, Robert S.

    1996-10-01

    Ce doped and undoped SrxBa1-xNb2O6 (SBN) fibers grown by the laser heated pedestal growth (LHPG) technique in Stanford University were investigated by 2D scanning electron microprobe analysis. The SBN fibers grown along c [001] or a [100] axes often show radially distributed optical inhomogeneities (core effects) of varying magnitude. Ba enrichment and Sr reduction were primarily detected in the core which can be qualitatively described by a complex-segregation effect. This defect structure as a complex-congruency related phenomenon modified by the composition-control mechanism of LHPG system. Its radial dependence of effective segregation coefficient is described by the modified Burton-Prim- Slichter equation.

  10. Photorefractive effects in polymer dissolved liquid crystal composites dopes with fullerene derivatives

    NASA Astrophysics Data System (ADS)

    Ono, Hiroshi; Hasebe, Ryoya; Sasaki, Tomoyuki; Noda, Kohei; Kawatsuki, Nobuhiro

    2013-07-01

    We investigated the photorefractive performance of the polymer dissolved liquid crystalline composite (PDLCC), in which liquid crystalline polymer and low-molar-mass liquid crystal are miscible without phase separation, doped with three kinds of fullerene derivatives with different length of alkyl groups. The photorefractive performance was improved for the photorefractive PDLCC doped with fullerene derivatives with long length of alkyl groups. The photorefractive grating formation originates in the cooperative reorientation of the liquid crystalline director and the space charge field was estimated using the elastic continuum theory and the field for the PDLCC doped with the functionalized fullerene with longer alkyl side groups was larger than that for the PDLCC doped with conventional fullerene C60.

  11. Orientation-Enhanced Photorefractive Effect in PVK-PBA:DR1:TNF Polymer

    NASA Astrophysics Data System (ADS)

    Li, Lu-Ying; Zhao, You-Yuan; Li, Fu-Ming; Yang, Jian; Chen, Guo-Rong; Wang, Chang-Chun

    2004-08-01

    We developed a novel photorefractive (PR) polymer PVK-PBA:DR1:TNF, and its film sample was prepared with outstanding performance by using the method of combination of vacuum saturated vapour resolving with vacuum hot-pressing. The sample exhibits distinctive PR properties with the two-beam coupling coefficient up to 140 cm-1 and four-wave mixing (FWM) diffraction efficiency above 1.5% in the absence of applied external electric field. The designed experiments, including measurements of the second-order nonlinear coefficient and birefringence as well as the relationship between the diffraction efficiencies of the FWM and the external bias field, were performed to understand the underlying mechanism, because this phenomenon cannot be explained by the conventional PR theories. It is presented that because of its high orientational mobility and large dipole moment, the polymer produces the photovoltaic effect under the irradiation of laser to induce a space-charge field so as to engender the PR effect under zero or low external fields. A model based on the assumption was established and the simulation agrees well with the experimental results.

  12. 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.

  13. 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.

  14. High-speed depth-sectioned wide-field imaging using low-coherence photorefractive holographic microscopy

    NASA Astrophysics Data System (ADS)

    Dunsby, C.; Gu, Y.; Ansari, Z.; French, P. M. W.; Peng, L.; Yu, P.; Melloch, M. R.; Nolte, D. D.

    2003-04-01

    Low-coherence photorefractive holography has the potential to acquire wide-field coherence-gated images at frame rates approaching 1000 frames/s, including through scattering media. We present a quantitative analysis of the system optimization and limits of performance for coherence-gated imaging through scattering media using photorefractive holography and compare this performance to direct CCD detection. We show that, for high optical quality recording photorefractive multiple quantum well devices, photorefractive holography has the potential to provide a higher dynamic range than is possible with direct CCD-based detection.

  15. Laser Spectroscopy Characterization of Materials for Frequency Agile Solid State Laser Systems

    DTIC Science & Technology

    1991-03-15

    as well as Nd3 +-doped garnets and germinates and Ho 3 +-doped fluorides. In addition, pfhotoreractlve processes were studied in potassium niobate...characterization of the properties of energy migration and radiationless relaxation processes in Cr3+-doped laser crystals; (5) The characterization of the... processes such as energy migration, multiphoton absorption, radiationless relaxation, and the photorefractive effect in materials with potential applications

  16. Airy beam self-focusing in a photorefractive medium

    PubMed Central

    Wiersma, Noémi; Marsal, Nicolas; Sciamanna, Marc; Wolfersberger, Delphine

    2016-01-01

    The unique bending and shape-preserving properties of optical Airy beams offer a large range of applications in for example beam routing, optical waveguiding, particle manipulation and plasmonics. In these applications and others, the Airy beam may experience nonlinear light-matter interactions which in turn modify the Airy beam properties and propagation. A well-known example is light self-focusing that leads to the formation of spatial soliton. Here, we unveil experimentally the self-focusing properties of a 1D-Airy beam in a photorefractive crystal under focusing conditions. The transient evolution involves both self-bending and acceleration of the initially launched Airy beam due to the onset of an off-shooting soliton and the resulting nonlocal refractive index perturbation. Both the transient and stationary self-focusing properties can be tuned by varying the bias electric field, the injected Airy beam power and the background illumination. PMID:27731356

  17. Airy beam self-focusing in a photorefractive medium

    NASA Astrophysics Data System (ADS)

    Wiersma, Noémi; Marsal, Nicolas; Sciamanna, Marc; Wolfersberger, Delphine

    2016-10-01

    The unique bending and shape-preserving properties of optical Airy beams offer a large range of applications in for example beam routing, optical waveguiding, particle manipulation and plasmonics. In these applications and others, the Airy beam may experience nonlinear light-matter interactions which in turn modify the Airy beam properties and propagation. A well-known example is light self-focusing that leads to the formation of spatial soliton. Here, we unveil experimentally the self-focusing properties of a 1D-Airy beam in a photorefractive crystal under focusing conditions. The transient evolution involves both self-bending and acceleration of the initially launched Airy beam due to the onset of an off-shooting soliton and the resulting nonlocal refractive index perturbation. Both the transient and stationary self-focusing properties can be tuned by varying the bias electric field, the injected Airy beam power and the background illumination.

  18. 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)

  19. 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)

  20. Photorefractive polymer composite trapping properties and a link with chromophore structure

    NASA Astrophysics Data System (ADS)

    West, K. S.; West, D. P.; Rahn, M. D.; Shakos, J. D.; Wade, F. A.; Khand, K.; King, T. A.

    1998-12-01

    The photorefractive properties and the phase stability of polymer composites are dependent on the detail of the alkyl chain substituent attached to the electro-optic dye within the composite. Photorefractive composites based on poly (N-vinylcarbazole) (PVK), sensitized with trinitrofluorenone (TNF) and mixed with a concentration of 47.5 wt. % of electro-optic dye have been tested for photorefractive performance. Two alternative azo dyes of identical molecular weight have been used to produce alternative composites; both dyes were modified to suppress spatial isomerism and incorporated an eight carbon alkyl chain at the electropositive end of the chromophore: either a straight octyl chain or a branched ethylhexyl chain was substituted. The reorientational enhancement of photorefractive performance is similar in the composites resulting from these dyes. The dye with a straight octyl chain led to a composite with improved holographic performance. The dye with a branched ethylhexyl chain led to a composite exhibiting lower diffraction efficiency, but with superior phase stability. A tentative explanation is offered for these differences based on the shape of the alkyl substituent and its effect on a trapping mechanism involving the dye molecules and the sensitisor anions in PVK:TNF-based photorefractive composites.

  1. Two beam energy exchange in hybrid liquid crystal cells with photorefractive field controlled boundary conditions

    NASA Astrophysics Data System (ADS)

    Reshetnyak, V. Yu.; Pinkevych, I. P.; Subota, S. I.; Evans, D. R.

    2016-09-01

    We develop a theory describing energy gain when two light beams intersect in a hybrid nematic liquid crystal (LC) cell with photorefractive crystalline substrates. A periodic space-charge field induced by interfering light beams in the photorefractive substrates penetrates into the LC layer and reorients the director. We account for two main mechanisms of the LC director reorientation: the interaction of the photorefractive field with the LC flexopolarization and the director easy axis at the cell boundaries. It is shown that the resulting director grating is a sum of two in-phase gratings: the flexoelectric effect driven grating and the boundary-driven grating. Each light beam diffracts from the induced gratings leading to an energy exchange between beams. We evaluate the signal beam gain coefficient and analyze its dependence on the director anchoring energy and the magnitude of the director easy axis modulation.

  2. A novel optic bistable device with very low threshold intensity using photorefractive films

    NASA Astrophysics Data System (ADS)

    Wang, Sean X.; Sun, Yuankun; Trivedi, Sudhir B.; Li, Guifang

    1994-08-01

    Brimrose Corporation of America reports the successful completion of the SBIR Phase I research in low-threshold intensity optical bistable devices using photorefractive nonlinearity. A thin photorefractive film optical bistable device was proposed in the Phase I proposal. The feasibility of this device was theoretically investigated. The theoretical feasibility study formulates the materials requirements in such a kind of configuration for Phase II research. In addition, we have proposed and investigated another configuration of optical bistable devices that do not require advanced photorefractive materials, namely, the self-pumped phase conjugator. We have successfully demonstrated a low-threshold optical bistable operation in a KNSBN:CU crystal. To the best of our knowledge, the threshold of 650 mW/sq. cm is the lowest of its kind to be achieved so far.

  3. Microraman and Photorefractivity Study of Hafnium-Doped Lithium Niobate Crystals

    NASA Astrophysics Data System (ADS)

    Galinetto, Pietro; Rossella, Francesco; Minzioni, Paolo; Razzari, Luca; Cristiani, Ilaria; Degiorgio, Vittorio; Kokanyan, Edvard P.

    We present an investigation of the properties of HfO2-doped lithium niobate crystals, in view of their possible utilization as low-photorefractivity crystals for wavelength converters operating at room temperature. MicroRaman measurements indicate that the linewidth of a specific mode can be used as a local indicator of crystal composition, and show that the grown crystals present very good uniformity. The mechanism by which the photorefractivity is strongly reduced when the HfO2 concentration is above 4 mol% is studied by combining measurements of birefringence variation, under green-light illumination, with electrical phototransport data.

  4. Optical trapping and manipulation of metallic micro/nanoparticles via photorefractive crystals.

    PubMed

    Zhang, Xinzheng; Wang, Junqiao; Tang, Baiquan; Tan, Xinhui; Rupp, Romano A; Pan, Leiting; Kong, Yongfa; Sun, Qian; Xu, Jingjun

    2009-06-08

    A simple method to trap and manipulate metallic micro/nano-particles on the surface of photorefractive crystals is proposed. After inducing inhomogeneous charge density and space-charge fields in photorefractive crystals by non-uniform illumination, both uncharged and charged metallic particles can be trapped on the illuminated surface due to dielectrophoretic force and electrophoretic force, respectively. A transition from dielectrophoresis to electrophoresis is observed when manipulating nano-silver particles with high surface space-charge field. Our results show that this method is simple and effective to form surface microstructures of metallic particles.

  5. Image feature extraction with various wavelet functions in a photorefractive joint transform correlator

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Cartwright, C. M.; Ding, M. S.; Gillespie, W. A.

    2000-11-01

    The wavelet transform has found a lot of uses in the field of optics. We present an experimental realization of employing variant wavelet filters into the object space of a photorefractive joint transform correlator to realize image feature extraction. The Haar's wavelet, Roberts gradient and Mexican-hat wavelet are employed in the experiment. Because of its good optical properties, the photorefractive crystal Bi 12SiO 20 is used as the dynamic holographic medium in the Fourier plane. Both scene and reference have been detour-phase encoded in a liquid crystal television in the input plane. Computer simulations, experimental results and analysis are presented.

  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. Quickly updatable hologram images with high performance photorefractive polymer composites

    NASA Astrophysics Data System (ADS)

    Tsutsumi, Naoto; Kinashi, Kenji; Nonomura, Asato; Sakai, Wataru

    2012-02-01

    We present here quickly updatable hologram images using high performance photorefractive (PR) polymer composite based on poly(N-vinyl carbazole) (PVCz). PVCz is one of the pioneer materials for photoconductive polymer. PVCz/7- DCST/CzEPA/TNF (44/35/20/1 by wt) gives high diffraction efficiency of 68 % at E = 45 V/μm with fast response speed. Response speed of optical diffraction is the key parameter for real-time 3D holographic display. Key parameter for obtaining quickly updatable hologram images is to control the glass transition temperature lower enough to enhance chromophore orientation. Object image of the reflected coin surface recorded with reference beam at 532 nm (green beam) in the PR polymer composite is simultaneously reconstructed using a red probe beam at 642 nm. Instead of using coin object, object image produced by a computer was displayed on a spatial light modulator (SLM) is used as an object for hologram. Reflected object beam from a SLM interfered with reference beam on PR polymer composite to record a hologram and simultaneously reconstructed by a red probe beam. Movie produced in a computer was recorded as a realtime hologram in the PR polymer composite and simultaneously clearly reconstructed with a video rate.

  8. Highly transparent and birefringent chromophores for organic photorefractive materials

    NASA Astrophysics Data System (ADS)

    Wortmann, R.; Glania, C.; Krämer, P.; Lukaszuk, K.; Matschiner, R.; Twieg, R. J.; You, F.

    1999-07-01

    A series of chromophores for application in organic photorefractive (PR) materials is investigated by electro-optical absorption measurements (EOAM). This experimental technique yields information on the transition dipole moment μag, the ground-state dipole moment μg, and the change of the dipole moment upon optical excitation Δ μ within the intense charge transfer (CT) band of the dyes. It is shown that the results of the EOAM experiment allow us to estimate the PR figures-of-merits (FOMs) of the chromophores by either perturbational two-level equations or Kramers-Kronig transformation. In particular, chromophores based on the heterocyclic dihydropyran and dihydropyridine groups in combination with dicyano and cyanocarboxy acceptor units were investigated. These donor-acceptor pairs yield chromophores close to the `cyanine limit' that is characterized by a small dipole difference, but a large ground-state dipole moment and a large polarizability anisotropy. This leads to very high PR FOMs of the new PR chromophores that are demonstrated to be superior to conventional second-order nonlinear optical (NLO) chromophores in situations where the medium has a low glass transition.

  9. Influence of chromophore solubility on optical absorption and two-beam coupling gain in guest-host photorefractive polymer composites

    NASA Astrophysics Data System (ADS)

    Carlen, C. R.; McGee, D. J.

    1998-07-01

    Recently developed photorefractive materials such as PVK:TNF:ECZ:DMNPAA are based on polymers doped with nonlinear optical chromophores. The high chromophore concentration necessary for macroscopic nonlinear optical effects necessitates investigation of methods to enhance chromophore solubility in the host polymer. We have modified the chromophore DMNPAA producing two new chromophores DMNPAPOE and DMNPAPBE with different solubilities in the polymer. Two-wave mixing experiments indicate that composites containing these two chromophores are photorefractive. Absorption measurements indicate that polymer composites doped with DMNPAPBE exhibit a significantly different rate of opacity development than composites doped with DMNPAPOE, demonstrating the role of chromophore solubility in the development of enhanced lifetime photorefractive polymer composite materials.

  10. The Role of Adaptive Photorefractive Power Limiting on Acousto-Optic Radio Frequency (RF) Signal Excision

    DTIC Science & Technology

    2001-12-01

    Adaptive RF interference reduction for broadband communication systems continues to be problematic. The acousto - optic RF signal excision system...novel photorefractive optical power limiting device to achieve adaptive notch filtering, and multi- channel acousto - optic deflection to achieve angle...of-arrival signal discrimination at the notch filter. This dissertation describes basic principles of acousto - optic RF signal excision, including

  11. 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.

  12. High-Capacity Photorefractive Neural Network Implementing a Kohonen Topological Map

    NASA Astrophysics Data System (ADS)

    Frauel, Yann; Pauliat, Gilles; Villing, André; Roosen, Gérald

    2001-10-01

    We designed and built a high-capacity neural network based on volume holographic interconnections in a photorefractive crystal. We used this system to implement a Kohonen topological map. We describe and justify our optical setup and present some experimental results of self-organization in the learning database.

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

    SciTech Connect

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

    2016-09-01

    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. As a result, it is anticipated that this approach can play a significant role in the eventual commercialization of this class of materials.

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

    DOE PAGES

    Moon, Jong -Sik; Stevens, Tyler E.; Monson, Todd C.; ...

    2016-09-01

    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

  15. 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

  16. 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.

  17. Matrix-vector multiplication in thin photorefractive GaAs crystals

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Gheen, Gregory

    1988-01-01

    Optical matrix-vector multiplication using four-wave mixing in a thin photorefractive GaAs crystal is demonstrated. Using a thin wafer of GaAs offers the potential to integrate the encoding spatial light modulators directly on the wave-mixing medium.

  18. Novel ultrafast tunable solid state lasers for real-world applications including medical imaging

    NASA Astrophysics Data System (ADS)

    Barry, Nicholas P.; Dainty, Christopher; Dowling, Keith; French, Paul M. W.; Hyde, Sam C. W.; Jones, Richard; Mellish, Richard; Sutherland, J. M.; Taylor, J. R.; Tong, Y. P.; Chai, Bruce H. T.; van den Poel, Carel J.; Valster, Adriaan

    1997-11-01

    This paper reviews ultrafast Kerr Lens Mode-locked solid- state lasers with particular emphasis on all-solid-state diode-pumped laser technology which has the potential to provide low-cost compact devices for ultrafast instrumentation, particularly for biomedical applications.We have demonstrated the use of ultrafast solid-state lasers for 3D imaging through turbid media using time-gated photorefractive holography, and for fluorescence lifetime imaging.

  19. 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.

  20. Ultrasound-modulated optical imaging using a powerful long pulse laser.

    PubMed

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

    2008-08-18

    Ultrasound-modulated optical imaging (or tomography) is an emerging biodiagnostic technique which provides the optical spectroscopic signature and the localization of an absorbing object embedded in a strongly scattering medium. We propose to improve the sensitivity of the technique by using a pulsed single-frequency laser to raise the optical peak power applied to the scattering medium and thereby collect more ultrasonically tagged photons. Moreover, when the detection of tagged photons is done with a photorefractive interferometer, the high optical peak power reduces the response time of the photorefractive crystal below the speckle field decorrelation time. Results obtained with a GaAs photorefractive interferometer are presented for 30- and 60-mm thick scattering media.

  1. Investigation of optical photorefractive properties of Zr:Fe:LiNbO 3 crystals

    NASA Astrophysics Data System (ADS)

    Zhou, Zifan; Wang, Biao; Lin, Shaopeng; Li, Yilun; Wang, Kun

    2012-03-01

    A series of Zr:Fe:LiNbO 3 crystals with various levels of ZrO 2 doping were grown by Czochraski technique. The optical damage resistance and photorefractive properties were deeply explored. The results showed that the ability optical damage resistance increased remarkably when the concentration of ZrO 2 is over threshold concentration, but which is lower than that of traditional damage resistant additive MgO. While, the holographic storage properties can be greatly enhanced by proper level of ZrO 2 doping in Fe:LiNbO 3. In terms of ions' site occupation model, the photo-damage resistant ability enhancement and the change of the photorefractive properties were discussed.

  2. Numerical method for an analysis of nonlinear light propagation in photorefractive media--time nonlocal approach.

    PubMed

    Ziółkowski, Andrzej

    2014-12-15

    Nonlinear light propagation in photorefractive media can be analyzed by numerical methods. The presented numerical approach has regard to the effects of time nonlocality. Two algorithms are presented, and compared in terms of physical results and computing times. The possibility to address the issue of time nonlocality in two ways is attributed to the fact that, it is possible to completely separate carrier dynamics evaluation and wave equation calculation. This in turn, allows to choose a short integration time for carrier dynamics and a longer one to solve the wave equation. The tests of the methods were carried out for a one-carrier model that describes most of photorefractive media, and for a model with bipolar transport and hot electron effect, used in descriptions of semiconductor materials.

  3. Photorefractive Three-Dimensional Disks for Optical Data Storage and Artificial Neural Networks

    NASA Astrophysics Data System (ADS)

    Li, Hsin-Yu Sidney

    This thesis is on the application of 3-D photorefractive crystals disks for holographic optical data storage and optical neural networks. Chapter 1 gives some introductory background and motivation for the materials given in this thesis. In Chapter 2, the coupled-mode analysis and Born's approximation in anisotropic crystals is reviewed. The results are similar to that of isotropic materials. However, there are approximations that are often neglected in the literature. Chapter 3 starts with the description of the holographic 3-D disk for data storage, and analyzes the various alignment errors and tolerance problems for a 3-D disk system. Of particular interest is the effects in image reconstruction caused by rotational angle error. An optimum configuration is found that minimizes this error. Chapter 4 examines the data storage density of 3-D disks and volume holographic storage systems that utilize wavelength/angle and spatial multiplexing. The maximum storage density and the geometry that achieves this density is derived. Chapter 5 discusses the diffraction efficiency of 3-D disks fabricated with photorefractive crystals. Practical geometries and crystal orientations for achieving maximum uniform diffraction efficiency are given and compared to the maximum obtainable diffraction efficiencies using arbitrary cut crystals. Experimental results are shown. Also derived in this chapter are the double grating effect from crystal anisotropy, and the optimum configuration for getting maximum diffraction efficiency using the 90 degree recording geometry. The Khuktarev band-transport model of the photorefractive effect is examined briefly with emphasis on the anisotropy of the material. The proper expression for the permittivity term in the space-charge field formula is derived. Chapter 6 gives an example of an optical neural network that uses photorefractive crystals. It is the real time face-recognition system. The setup and experiments are described. Some properties of

  4. Phase conjugation, isotropic and anisotropic higher order diffraction generation, and image correlation using photorefractive barium titanate

    NASA Astrophysics Data System (ADS)

    Buranasiri, Prathan

    2005-04-01

    Using barium titanate as the photorefractive material, we demonstrate phase conjugation, beam coupling, higher diffraction order generation. At small incident angles less than 0.015 radian, both codirectional isotropic self-diffraction (CODIS) and contradirectional isotropic self-diffraction (CONDIS) are generated simultaneously. At bigger incident angles approximately more than 0.2094 radian, only codirectional anisotropic-self diffraction (CODAS) are generated. On going imaging correlation is also showing.

  5. 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.

  6. Two-beam energy exchange in a hybrid photorefractive-flexoelectric liquid-crystal cell.

    PubMed

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

    2010-03-01

    We develop a semiquantitative theory to describe the experimentally observed energy gain when two light beams intersect in hybrid organic-inorganic photorefractives. These systems consist of a nematic liquid-crystal (LC) layer placed between two photorefractive windows. A periodic space-charge field is induced by the interfering light beams in the photorefractive windows. The field penetrates into the LC, interacting with the nematic director and giving rise to a diffraction grating. LC flexoelectricity is the principal physical mechanism driving the grating structure. Each light beam diffracts from the induced grating, leading to an apparent energy gain and loss within each beam. The LC optics is described in the Bragg regime. In the theory the exponential gain coefficient is a product of a beam interference term, a flexoelectricity term and a space-charge term. The theory has been compared with results of an experimental study on hybrid cells filled with the LC mixture TL 205. Experimentally the energy gain is maximal at much lower grating wave numbers than is predicted by naïve theory. However, if the director reorientation is cubic rather than linear in the space-charge field term, then good agreement between theory and experiment can be achieved using only a single fitting parameter. We provide a semiquantitative argument to justify this nonlinearity in terms of electric-field-induced local phase separation between different components of the liquid crystal.

  7. 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

  8. Two-wave mixing and energy transfer in BaTiO3 application to laser beamsteering

    NASA Astrophysics Data System (ADS)

    Rak, D.; Ledoux, I.; Huignard, J. P.

    1984-03-01

    Energy transfer between the two recording beams in a BaTiO3 photorefractive crystal is analyzed as a function of the following parameters: incident beams ratio, spatial frequency, pump beam intensity. Exponential gain coefficients of approximately 20/cm are reached for optimized holographic recording conditions. Application of the energy transfer to a new method of laser beam deflection is proposed.

  9. Ultrasonic vibration modal analysis of ICF targets using a photorefractive optical lock-in

    NASA Astrophysics Data System (ADS)

    Hale, Thomas C.; Asaki, Thomas J.; Telschow, Kenneth L.; Hoffer, Jim

    1998-03-01

    A photorefractive optical lock-in is discussed in relation to ultrasonic vibration modal analysis of inertial confinement fusion (ICF) targets. In this preliminary report, the method is used to analyze specimens with similar response characteristics to ICF targets with emphasis on both the displacement and frequency resolution of the technique. The experimental method, based on photorefractive frequency domain processing, utilizes a synchronous detection approach to measure phase variations in light scattered from optically rough, continuously vibrating surfaces with very high, linear sensitivity. In this photorefractive four-wave mixing technique, a small, point image of the object surface is made to interfere with a uniform, frequency modulated reference beam inside a Bismith Silicon Oxide crystal. Optical interference and the photorefractive effect of electronic charge redistribution leads to the formation of a refractive index grating in the medium that responds to the modulated beams at a frequency equal to the difference between the signal and reference frequencies. By retro-reflecting the reference beam back into the crystal, a diffracted beam, counter-propagating with respect to the original transmitted beam, is generated. Using a beamsplitter, the counter-propagating beam can be picked-off and deflected toward a photodetector. The intensity of this diffracted beam is shown to be a function of the first-order ordinary Bissel function, and therefore linearly dependent on the vibration displacement induced phase modulation depth (delta) , for small (delta) ((delta) < 4 (pi) (xi) /(lambda) < < 1) where (xi) is the vibration displacement and (lambda) is the source wavelength; analytical description and experimental verification of this linear response are given. The technique is applied to determine the modal characteristics of a rigidly clamped disc from 10 kHz to 100 kHz, a frequency range similar to that used to characterize ICF targets. The results

  10. 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.

  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. Picosecond photorefractive response of GaAs:EL2, InP:Fe, and CdTe:V.

    PubMed

    Valley, G C; Dubard, J; Smirl, A L; Glass, A M

    1989-09-01

    Measurements and theoretical calculations are presented for the photorefractive effect in three semi-insulating semiconductors (GaAs:EL2, InP:Fe, and CdTe:V) using 29-psec pulses at a wavelength of 1.06 microm. The photorefractive gain is largest in the CdTe crystal and smallest in our InP sample. The major differences between the materials responsible for this are the electro-optic coefficients, the mobilities, the absorption coefficients, and the amount of electron-hole competition.

  13. Roles of resonance and dark irradiance for infrared photorefractive self-focusing and solitons in bipolar InP:Fe

    SciTech Connect

    Fressengeas, N.; Khelfaoui, N.; Dan, C.; Wolfersberger, D.; Montemezzani, G.; Leblond, H.; Chauvet, M.

    2007-06-15

    This paper shows experimental evidence of photorefractive steady state self-focusing in InP:Fe for a wide range of intensities, at both 1.06 and 1.55 {mu}m. To explain those results, it is shown that despite the bipolar nature of InP:Fe where one photocarrier and one thermal carrier are to be considered, the long standing one photocarrier model for photorefractive solitons can be usefully applied. The relationship between the dark irradiance stemming out of this model and the known resonance intensity is then discussed.

  14. 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

  15. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    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.

  17. 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

    2016-02-03

    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.

  18. 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.

  19. Photorefractive two-beam coupling optimal thresholding filter for additive signal-dependent noise reduction

    NASA Astrophysics Data System (ADS)

    Fu, Jack; Khoury, Jehad; Cronin-Golomb, Mark; Woods, Charles L.

    1995-01-01

    Computer simulations of photorefractive thresholding filters for the reduction of artifact or dust noise demonstrate an increase in signal-to-noise ratio (SNR) of 70% to 95%, respectively, of that provided by the Wiener filter for inputs with a SNR of approximately 3. These simple, nearly optimal filters use a spectral thresholding profile that is proportional to the envelope of the noise spectrum. Alternative nonlinear filters with either 1/ nu or constant thresholding profiles increase the SNR almost as much as the noise-envelope thresholding filter.

  20. Spatial solitons in biased photovoltaic photorefractive materials with the pyroelectric effect

    NASA Astrophysics Data System (ADS)

    Katti, Aavishkar; Yadav, R. A.

    2017-01-01

    Spatial solitons in biased photorefractive media due to the photovoltaic effect and the pyroelectric effect are investigated. The pyroelectric field considered is induced due to the heating by the incident beam's energy. These solitons can be called screening photovoltaic pyroelectric solitons. It is shown that the solitons can exist in the bright and dark realizations. The conditions for formation of these solitons are discussed. Relevant example is considered to illustrate the self trapping of such solitons. The external electric field interacts with the photovoltaic field and the pyroelectric field to either support or oppose the self trapping.

  1. Evaluation of photoelectric processes in photorefractive crystals via the exposure characteristics of light diffraction.

    PubMed

    Kadys, A; Gudelis, V; Sudzius, M; Jarasiunas, K

    2005-01-12

    We demonstrate a novel way to analyse carrier recombination and transport processes in photorefractive semiconductors via the exposure characteristics of light induced diffraction. The results of a picosecond four-wave mixing on free carrier gratings in semi-insulating GaAs crystals at various grating periods and modulation depths of a light interference pattern are discussed. The role of a deep-trap recharging in carrier diffusion and recombination is sensitively revealed through a feedback effect of a space-charge field to non-equilibrium carrier transport.

  2. Observation of bright spatial photorefractive solitons in a planar strontium barium niobate waveguide.

    PubMed

    Kip, D; Wesner, M; Shandarov, V; Moretti, P

    1998-06-15

    We have obtained stationary bright spatial solitons in a planar photorefractive strontium barium niobate waveguide for visible light ranging from 514.5 to 780 nm. Even for larger wavelengths (lambda=1047 nm) strong self-focusing of the beam was observed; however, input power had to be some orders of magnitude higher than for visible light for self-focusing to occur. Furthermore, we found transient self-trapping of red light (lambda=632.8 nm) that corresponds to the formation of bright quasi-steady-state solitons.

  3. 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.

  4. 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.

  5. Excitation Energy and Temperature Dependence of the Phase Coherent Photorefractive Effect

    NASA Astrophysics Data System (ADS)

    Kabir, A.; Wagner, H. P.

    2011-12-01

    We investigate the influence of excitation energy and temperature on the phase coherent photorefractive (PCP) effect in ZnSe quantum wells. At temperatures below 35 K and nearly exciton resonant excitation the formation of trions suppresses the PCP effect. At lower excitation energies increasing space-charge-fields reduce the trion binding energy which leads to an enhanced thermal ionization of trions resulting in a PCP signal. Due to the thermal dissociation of trions at temperatures exceeding 40 K a strong PCP effect occurs even at nearly resonant excitation.

  6. Photorefractive gain in GaAs under a dc electric field

    NASA Technical Reports Server (NTRS)

    Liu, Duncan T. H.; Cheng, Li-Jen; Rau, Mann-Fu; Wang, Faa-Ching

    1988-01-01

    This paper reports on the first observation of a photorefractive gain coefficient as high as 2.6/cm in the undoped liquid-encapsulated Czochralski-grown GaAs crystals at 1.06 microns under a dc electric field of 13 kV/cm without using the moving grating technique.The absorption coefficient of the crystals used is 1.3/cm, showing that a net gain has been achieved. This measured gain coefficient is close to the predicted theoretical value.

  7. Enhanced beam coupling modulation using the polarization properties of photorefractive GaAs

    NASA Technical Reports Server (NTRS)

    Partovi, Afshin; Garmire, Elsa M.; Cheng, Li-Jen

    1987-01-01

    Observation is reported of a rotation in the polarization of the two photorefractive recording beams in GaAs for a configuration with the internally generated space-charge field along the line 110 crystallographic orientation. This rotation is a result of simultaneous constructive and destructive beam coupling in each beam for the optical electric field components along the two electrooptically induced principal dielectric axes of the crystal. By turning one of the beams on and off, the intensity of the other beam after the crystal and a polarization analyzer can be modulated by as much as 500 percent. This result is of particular importance for optical information processing applications.

  8. Photorefractive Properties of Doped BaTiO3 and SBN

    DTIC Science & Technology

    1991-12-01

    tkucolendion of irrar’e Send cimr ais r rgwr this bude, esrtme aof tref aspet of •ns cObotic of Hi ~arn at ck a ggesbo far rnecid *xr tsU b to WaM anr...were studied. Isotropic scattering of a single intense pump beam was observed and modeled. Numerical calculations, performed using material...be constants. Several novel photorefractive scattering processes were also studied. Isotropic scattering of a single intense pump beam was observed and

  9. Photorefractive Tungsten Bronze Crystals for Optical Limiters and Filters.

    DTIC Science & Technology

    1996-01-01

    3. High temperature growths (up to 1500 °C) cause volatilization and oxidation-reduction (Nb5+ to Nb4 +) problems. 4. Cracking of crystals when...2 Dye Laser dT2 0tetu iati Cr + Cr3+, Fe3+, Rh3+, Nb4 + Figure 3.1 -- The effect of dopant site preference on spectral response. The circled numbers...PARAMETERS __________________________- Completely oxidize Nb Dopants andTheir Site Preference 1APPROACH - Double Doping Scheme Control of the Nb5+ to Nb4

  10. 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.}

  11. Lasers.

    PubMed

    Passeron, T

    2012-12-01

    Lasers are a very effective approach for treating many hyperpigmented lesions. They are the gold standard treatment for actinic lentigos and dermal hypermelanocytosis, such as Ota nevus. Becker nevus, hyperpigmented mosaicisms, and lentigines can also be successfully treated with lasers, but they could be less effective and relapses can be observed. However, lasers cannot be proposed for all types of hyperpigmentation. Thus, freckles and café-au-lait macules should not be treated as the relapses are nearly constant. Due to its complex pathophysiology, melasma has a special place in hyperpigmented dermatoses. Q-switched lasers (using standard parameters or low fluency) should not be used because of consistent relapses and the high risk of post-inflammatory hyperpigmentation. Paradoxically, targeting the vascular component of the melasma lesion with lasers could have a beneficial effect. However, these results have yet to be confirmed. In all cases, a precise diagnosis of the type of hyperpigmentation is mandatory before any laser treatment, and the limits and the potential side effects of the treatment must be clearly explained to patients.

  12. [Lasers].

    PubMed

    Passeron, T

    2012-11-01

    Lasers are a very effective approach for treating many hyperpigmented lesions. They are the gold standard treatment for actinic lentigos and dermal hypermelanocytosis, such as Ota nevus. Becker nevus, hyperpigmented mosaicisms, and lentigines can also be successfully treated with lasers, but they could be less effective and relapses can be observed. However, lasers cannot be proposed for all types of hyperpigmentation. Thus, freckles and café-au-lait macules should not be treated as the relapses are nearly constant. Due to its complex pathophysiology, melasma has a special place in hyperpigmented dermatoses. Q-switched lasers (using standard parameters or low fluency) should not be used because of consistent relapses and the high risk of post-inflammatory hyperpigmentation. Paradoxically, targeting the vascular component of the melasma lesion with lasers could have a beneficial effect. However, these results have yet to be confirmed. In all cases, a precise diagnosis of the type of hyperpigmentation is mandatory before any laser treatment, and the limits and the potential side effects of the treatment must be clearly explained to patients.

  13. Excisional keratectomy combined with focal cryotherapy and amniotic membrane inlay for recalcitrant filamentary fungal keratitis: A retrospective comparative clinical data analysis.

    PubMed

    Chen, Yingxin; Gao, Minghong; Duncan, Joshua K; Ran, Di; Roe, Denise J; Belin, Michael W; Wang, Mingwu

    2016-11-01

    The aim of the present study was to investigate the efficacy of a novel surgical intervention, excisional keratectomy combined with focal cryotherapy and amniotic membrane inlay (EKCAI), for the treatment of recalcitrant filamentary fungal keratitis. A retrospective analysis was performed of patients who underwent excisional keratectomy combined with conjunctival flap inlay (EKCFI), EKCAI or therapeutic penetrating keratoplasty (TPK) from January 2006 to January 2011. Recalcitrance was determined as being unresponsive to standard medical antifungal therapy for at ≥1 week. Outcome measures among the three intervention modalities were compared. A total of 128 patients had a follow-up of ≥1 year after the primary intervention. The success rates of interventions at 1-year follow-up were 58.33% in the EKCFI group, 88.37% in the EKCAI group and 93.44% in the TPK group (P<0.0002). The preoperative visual acuity of the three groups were similar (P=0.6458), while the postoperative best-corrected visual acuity (BCVA) of patients without recurrence was significantly different among the three groups 3 months after surgery. The best postoperative BCVA was found in the TPK group, while the worst was in the EKCFI group. In conclusion, EKCAI does not require donor cornea, is straightforward surgically, and has a favorable success rate compared with EKCFI.

  14. Excisional keratectomy combined with focal cryotherapy and amniotic membrane inlay for recalcitrant filamentary fungal keratitis: A retrospective comparative clinical data analysis

    PubMed Central

    Chen, Yingxin; Gao, Minghong; Duncan, Joshua K.; Ran, Di; Roe, Denise J.; Belin, Michael W.; Wang, Mingwu

    2016-01-01

    The aim of the present study was to investigate the efficacy of a novel surgical intervention, excisional keratectomy combined with focal cryotherapy and amniotic membrane inlay (EKCAI), for the treatment of recalcitrant filamentary fungal keratitis. A retrospective analysis was performed of patients who underwent excisional keratectomy combined with conjunctival flap inlay (EKCFI), EKCAI or therapeutic penetrating keratoplasty (TPK) from January 2006 to January 2011. Recalcitrance was determined as being unresponsive to standard medical antifungal therapy for at ≥1 week. Outcome measures among the three intervention modalities were compared. A total of 128 patients had a follow-up of ≥1 year after the primary intervention. The success rates of interventions at 1-year follow-up were 58.33% in the EKCFI group, 88.37% in the EKCAI group and 93.44% in the TPK group (P<0.0002). The preoperative visual acuity of the three groups were similar (P=0.6458), while the postoperative best-corrected visual acuity (BCVA) of patients without recurrence was significantly different among the three groups 3 months after surgery. The best postoperative BCVA was found in the TPK group, while the worst was in the EKCFI group. In conclusion, EKCAI does not require donor cornea, is straightforward surgically, and has a favorable success rate compared with EKCFI. PMID:27882109

  15. 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.

  16. 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.

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

    DOE PAGES

    Moon, Jong-Sik; Liang, Yichen; Stevens, Tyler E.; ...

    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

  18. 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.

  19. 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.

  20. Refractive lenticule extraction (ReLEx) through a small incision (SMILE) for correction of myopia and myopic astigmatism: current perspectives

    PubMed Central

    Ağca, Alper; Demirok, Ahmet; Yıldırım, Yusuf; Demircan, Ali; Yaşa, Dilek; Yeşilkaya, Ceren; Perente, İrfan; Taşkapılı, Muhittin

    2016-01-01

    Small-incision lenticule extraction (SMILE) is an alternative to laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) for the correction of myopia and myopic astigmatism. SMILE can be performed for the treatment of myopia ≤−12 D and astigmatism ≤5 D. The technology is currently only available in the VisuMax femtosecond laser platform. It offers several advantages over LASIK and PRK; however, hyperopia treatment, topography-guided treatment, and cyclotorsion control are not available in the current platform. The working principles, potential advantages, and disadvantages are discussed in this review. PMID:27757010

  1. Sn vacancies in photorefractive Sn2P2S6 crystals: An electron paramagnetic resonance study of an optically active hole trap

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    Electron paramagnetic resonance (EPR) is used to identify the singly ionized charge state of the Sn vacancy ( VSn - ) in single crystals of Sn2P2S6 (often referred to as SPS). These vacancies, acting as a hole trap, are expected to be important participants in the photorefractive effect observed in undoped SPS crystals. In as-grown crystals, the Sn vacancies are doubly ionized ( VSn 2 - ) with no unpaired spins. They are then converted to a stable EPR-active state when an electron is removed (i.e., a hole is trapped) during an illumination below 100 K with 633 nm laser light. The resulting EPR spectrum has g-matrix principal values of 2.0079, 2.0231, and 1.9717. There are resolved hyperfine interactions with two P neighbors and one Sn neighbor. The isotropic portions of these hyperfine matrices are 167 and 79 MHz for the two 31P neighbors and 8504 MHz for the one Sn neighbor (this latter value is the average for 117Sn and 119Sn). These VSn - vacancies are shallow acceptors with the hole occupying a diffuse wave function that overlaps the neighboring Sn2+ ion and (P2S6)4- anionic unit. Using a general-order kinetics approach, an analysis of isothermal decay curves of the VSn - EPR spectrum in the 107-115 K region gives an activation energy of 283 meV.

  2. Synthesis of organic phenothiazine-based molecular glasses and effect of racemic/homochiral aliphatic chain on near-infrared photorefractive property

    NASA Astrophysics Data System (ADS)

    Liu, Yingliang; Fujimura, Ryushi; Ishida, Kazuki; Oya, Nobuhiro; Yoshie, Naoko; Shimura, Tsutomu; Kuroda, Kazuo

    2012-09-01

    Organic near-infrared photorefractive molecular glasses with a phenothiazine moiety are designed and synthesized through the introduction of linear, racemic/homochiral asymmetrically branched aliphatic chains into photorefractive chromophore as an auxiliary group. The compounds are characterized with 1H-NMR, IR, FAB-MS, UV-vis, TG, DSC, etc. The effect of different aliphatic chains on the absorption and thermal properties is investigated in detail. The molar absorption coefficiency at the absorption maximum wavelength showed that the homochiral asymmetrically branched aliphatic chain has a strong hypochromic effect in the dilute solution when it is introduced into photorefractive chromophore. The DSC measurement indicated that the introduction of asymmetrically branched aliphatic chain is the key issue to design organic molecular glasses whether it is racemic or homochiral. The effect of racemic/homochiral asymmetrically branched aliphatic groups on photorefractive property is investigated carefully with poly(N-vinylcarbazole) (PVK) as a photoconductor and with (2,4,7-trinitro-9-fluorenylidene) malononitrile (TNFM) as a photosensitizer. The results suggested that the racemic group is more beneficial to the improvement of photorefractive performance than the homochiral when the homochiral cannot induce rigid photorefractive chromophore to be much more ordered.

  3. Laser Phase Noise Reduction for Industrial Interferometric Applications

    NASA Astrophysics Data System (ADS)

    Dubois, Marc; Burr, Kent C.; Drake, Thomas E.

    2004-08-01

    Laser ultrasound is a technique used for the ultrasonic inspection of composites during manufacturing of advanced jet fighters. With this technique laser interferometry is used to detect ultrasonic displacements generated by a laser. In theory, the signal-to-noise ratio is proportional to the square root of the collected detection light. In practice, laser phase noise limits the signal-to-noise ratio above a certain collected light level. Two techniques are presented to decrease effects due to laser noise. In one technique the dual-cavity Fabry-Perot currently used is replaced by an interferometer based on a photorefractive crystal. The other technique has a high-finesse Sagnac cavity that filters the phase noise from the detection laser. Experimental results demonstrate that these two techniques significantly reduce limitations due to laser noise.

  4. Beam-steering and jammer-nulling photorefractive phased-array radar processor

    NASA Astrophysics Data System (ADS)

    Sarto, Anthony W.; Weverka, Robert T.; Wagner, Kelvin H.

    1994-06-01

    We are developing a class of optical phased-array-radar processors which use the large number of degrees-of-freedom available in 3D photorefractive volume holograms to time integrate the adaptive weights to perform beam-steering and jammer-cancellation signal-processing tasks for very large phased-array antennas. We have experimentally demonstrated independently the two primary subsystems of the beam-steering and jammer-nulling phased-array radar processor, the beam-forming subsystem and the jammer-nulling subsystem, as well as simultaneous main beam formation and jammer suppression in the combined processor. The beam-steering subsystem calculates the angle of arrival of a desired signal of interest and steers the antenna pattern in the direction of this desired signal by forming a dynamic holographic grating proportional to the correlation between the incoming signal of interest from the antenna array and the temporal waveform of the desired signal. This grating is formed by repetitively applying the temporal waveform of the desired signal to a single acousto-optic Bragg cell and allowing the diffracted component from the Bragg cell to interfere with an optical mapping of the received phased-array antenna signal at a photorefractive crystal. The diffracted component from this grating is the antenna output modified by an array function pointed towards the desired signal of interest. This beam-steering task is performed with the only a priori information being that of the knowledge of a temporal waveform that correlates well with the desired signal and that the delay of the desired signal remains within the time aperture of the Bragg cell. The jammer-nulling subsystem computes the angles-of- arrival of multiple interfering narrowband radar jammers and adaptively steers nulls in the antenna pattern in order to extinguish the jammers by implementing a modified LMS algorithm in the optical domain. This task is performed in a second photorefractive crystal where

  5. Discrete vector solitons in one-dimensional lattices in photorefractive media

    NASA Astrophysics Data System (ADS)

    Fitrakis, E. P.; Kevrekidis, P. G.; Malomed, B. A.; Frantzeskakis, D. J.

    2006-08-01

    We construct families of two-component spatial solitons in a one-dimensional lattice with saturable on-site nonlinearity (focusing or defocusing) in a photorefractive crystal. We identify 14 species of vector solitons, depending on their type (bright/dark), phase (in-phase/staggered), and location on the lattice (on/off-site). Two species of the bright/bright type form entirely stable soliton families, four species are partially stable (depending on the value of the propagation constant), while the remaining eight species are completely unstable. “Symbiotic” soliton pairs (of the bright/dark type), which contain components that cannot exist in isolation in the same model, are found as well.

  6. Improvement in photorefractivity of a polymeric composite doped with the electron-injecting material Alq3

    NASA Astrophysics Data System (ADS)

    Wei, Qun; Liu, Yihong; Chen, Zhijian; Huang, Maomao; Zhang, Jie; Gong, Qihuang; Chen, Xiaofang; Zhou, Qifeng

    2004-09-01

    A photorefractive composite composed of 8-pertyloxy-4' -cyanobiphenyl (8OCB)/N, N' -diphenyl-N, N' -bis(3-methylphenyl)-[1,1' -biphenyl]-4,4' -diamine (TPD)/2,4,7-trinitro-9-fluorenone (TNF)/tris(8-hydroxyquinoline) aluminium (Alq3)/polycarbonate plastic was fabricated. The additive of Alq3 in the composite leads to a larger two-beam coupling coefficient Ggr and shorter response time. Ggr over 330 cm-1 at an applied electric field of 26 V µm-1 was measured while Ggr of the sample without Alq3 was only 213 cm-1. It is presumed that the electron-injecting material Alq3 and charge-transporting material TPD form more effective traps in the composite, which leads to the improvement in the PR performance.

  7. Self-imaging, self-healing beams generated by photorefractive volume holography

    NASA Astrophysics Data System (ADS)

    Manigo, Jonathan P.; Guerrero, Raphael A.

    2015-10-01

    Self-imaging beams consisting of three-dimensional intensity voids are generated via photorefractive volume holography. Reconstruction of a volume hologram recorded at 594 nm is performed with a Bessel readout beam. The holographic output is similar in appearance to a Bessel beam, with the central spot oscillating between maximum and zero intensity over a propagation distance of 10 to 55 cm. The oscillation period for the on-axis intensity is 30 cm. The reconstruction is capable of self-healing, with a fully recovered central core after the beam propagates 40 cm. Dual-wavelength reconstruction at 632.8 nm produces an output beam with similar self-imaging and self-healing properties. A theoretical framework based on the interference of a plane wave and a Bessel beam simultaneously reconstructed from a volume hologram is able to describe our experimental results.

  8. Enhanced photorefractive performance of bulk cu-doped KNSBN crystals through surface electrostatic modification

    NASA Astrophysics Data System (ADS)

    Li, Liang; Zhang, Jingwen; Zhao, Hua

    2017-01-01

    The remarkable photorefractivity enhancement was observed and investigated in copper-doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 (Cu:KNSBN) crystals due to charge accumulation on the surface, stemming from electrostrictive effect. This electrostatic modification to the surface was studied with conventional two beam coupling experiment and over 17 high diffraction orders were observed. To estimate the amount of charge accumulation, the surface charge density was measured through direct current measurement using a close loop circuit. It was believed that a thin phase grating was responsible for the diffraction pattern, which was confirmed by the related reading experiment. Corresponding calculation and analysis were given to highlight the strong refractive index modulation of the gratings.

  9. Laser-spectroscopy investigations of materials for solid-state-laser systems. Final report, 16 January 1985-15 January 1988

    SciTech Connect

    Powell, R.C.

    1988-02-01

    Some of the results of major importance from this work are: (1) development of a method for producing laser-induced grating optical devices in glasses; (2) elucidation of the effects of Mg on inhibiting the photorefractive response of lithium niobate; (3) demonstration of tunable single-pass gain from a closed-shell ion in the visible spectral region; (4) demonstration of the decrease in fluorescence quenching in fiber crystals; (5) demonstration of the effects of thermal annealing on the infrared absorption and visible emission in Ti-sapphire laser crystals; and (6) measurement of the pump band to metastable-state relaxation rate in alexandrite laser crystals.

  10. Impact of the photorefractive and pyroelectric-electro-optic effect in lithium niobate on whispering-gallery modes.

    PubMed

    Leidinger, Markus; Werner, Christoph S; Yoshiki, Wataru; Buse, Karsten; Breunig, Ingo

    2016-12-01

    Whispering-gallery resonators made of undoped and MgO-doped congruently grown lithium niobate are used to study electro-optic refractive index changes. Hereby, we focus on the volume photovoltaic and the pyroelectric effect, both providing an electric field driving the electro-optic effect. Our findings indicate that the light-induced photorefractive effect, combining the photovoltaic and electro-optic effect, is present only in the non-MgO-doped lithium niobate for exposure with light having wavelengths of up to 850 nm. This leads to strong resonance frequency shifts of the whispering-gallery modes. No photorefractive effect was observed in the MgO-doped material. One has to be aware that surface charges induced by the pyroelectric effect result in a similar phenomenon and are present in both materials.

  11. Potential formalism of optical spatial soliton propagation in a two-photon photovoltaic-photorefractive material under open circuit condition

    NASA Astrophysics Data System (ADS)

    Akhouri, B. P.; Gupta, P. K.

    2014-04-01

    Propagation characteristics of optical spatial solitons in a two-photon photovoltaic-photorefractive medium under open circuit condition have been investigated using the formalism of a particle in a potential well. Optical nonlinearity has been evaluated using Castro-Camus model. Variational formalism has been employed to investigate the resulting modified nonlinear Schrödinger equation. Potential formalism has been examined to identify localized optical spatial solitons.

  12. Surgical correction of moderate myopia: which method should you choose? I. Radial keratotomy will always have a place.

    PubMed

    Rowsey, J J; Morley, W A

    1998-01-01

    This set of "Viewpoints" articles examines the relative merits of radial keratotomy (RK), photorefractive keratectomy (PRK), and laser assisted in-situ keratomileusis (LASIK). Drs. Rowsey and Morley review advances in RK techniques, long-term results, and complications, and explain why RK will remain a viable method for correction of moderate myopia, notably its minimal cost. Drs. Steinert and Bafna review both PRK and LASIK, discussing techniques and results and comparing their advantages and disadvantages with each other and with RK. Dr. Dutton, as "Viewpoints" section editor, summarizes clinical, technologic, and economic aspects of all three techniques, concluding that all will find a place among refractive surgeons for some time to come.

  13. Optical correlation using isotropic and anisotropic self diffraction using photorefractive material

    NASA Astrophysics Data System (ADS)

    Buranasiri, Prathan

    For two incident optical beams at different angles of incidence, a photorefractive cerium doped barium titanate crystal can facilitate different configurations of self-diffraction into higher orders. These configurations can be classified as isotropic and anisotropic, co-directional and contra-directional. Sometimes, a higher order resulting from an incident diverging object beam may comprise a converging beam, which then has the property of phase conjugation. Photorefractive fanning plays an important role in all these self-diffraction configurations. In this dissertation, we first explore the first higher order generated by forward three wave mixing. Only one higher order is observed when one of the incident beams is perpendicular to the surface of incidence. Not only the energy transfer via the first order grating has been observed but the energy transfer via the second order grating has been observed as well. With the angle between two incident beams less than 0.015 radians, the second configuration of self-diffraction has been investigated. With this configuration, codirectional isotropic self-diffraction (CODIS) and contradirectional isotropic self diffraction (CONDIS) have been observed. Phase conjugated beams which are responsible for CONDIS are the composite of mutual pumped phase conjugate (MPPC) and self pumped phase conjugate (SPPC). Due to the fanning effect, CONDIS usually forms before CODAS. In general, energy transfer between incident beams and CONDIS and CODIS occurs via first order and higher order gratings. For certain large but specific angles between the two incident extraordinarily polarized beams, it is possible to obtain anisotropic self-diffraction into ordinarily polarized higher orders. This third configuration for self-diffraction, called codirectional anisotropic self-diffraction (CODAS), can be generated most efficiently for the Bragg-matched case, although we have also observed CODAS with Bragg mismatch. In addition, CODAS has been

  14. High T(g) photorefractive polymers: influence of the chromophores' beta tensor.

    PubMed

    Acebal, P; Blaya, S; Carretero, L

    2004-11-01

    In this paper we study the effect of the chromophores' beta tensor active components on the diffraction efficiency of a high T(g) photorefractive polymer. In particular, we study the two simplest structures with nonvanishing dipole moment, the one-dimension push-pull systems, and the Lambda-shaped chromophores. We have developed a model that relate the diffraction efficiency expression with experimental conditions and microscopic properties of the molecules used. Using this model we determine the optimum experimental conditions for both kinds of chromophores and the criteria for the design of chromophores with improved microscopic properties. The model was also used to evaluate the diffraction efficiency of the chromophore Disperse Red 1 (DR1) with a good agreement with experimental data present in bibliography, and of other chromophores selected with the criteria derived from the model, using quantum mechanical calculations to obtain the microscopic properties. Using the designed chromophores diffraction efficiencies more than one order of magnitude higher than that calculated for DR1 with the experimental conditions has been obtained in simulations. These chromophores also exhibit a low dependency of eta on the electric field polarization in contrast to the DR1 or the low T(g) photoreactive materials.

  15. Simulating Photo-Refraction Images of Keratoconus and Near-Sightedness Eyes

    NASA Astrophysics Data System (ADS)

    Baker, Kevin; Lewis, James W. L.; Chen, Ying-Ling

    2004-11-01

    Keratoconus is an abnormal condition of the eye resulting from cone-shaped features on the cornea that degrade the quality of vision. These corneal features result from thinning and subsequent bulging due to intraocular pressure. The abnormal corneal curvature increases the refractive power asymmetrically and can be misdiagnosed by examiners as astigmatism and nearsightedness. Since corrective treatment is possible, early detection of this condition is desirable. Photo-refraction (PR) detects the retinal irradiance reflected from a single light source and is an inexpensive method used to identify refractive errors. For near- (far-) sighted eye, a crescent appears on the same (opposite) side of the light source. The capability of a PR device to detect keratoconus and to differentiate this condition from myopia was investigated. Using a commercial optical program, synthetic eye models were constructed for both near-sighted and keratoconus eyes. PR images of various eye conditions were calculated. The keratoconus cone shapes were modeled with typical published cone locations and sizes. The results indicate significant differences between the images of keratoconus and near-sighted eyes.

  16. Enhancement in the photorefractive performance of organic composites photosensitized with functionalized CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Liang, Yichen; Wang, Wei; Moon, Jong-Sik; Winiarz, Jeffrey G.

    2016-08-01

    Enhancement in the photorefractive (PR) performance of organic composites photosensitized by CdSe quantum dots (QCdSe) passivated with the charge-transport ligands, sulfonated triphenyldiamine (STPD), is reported. This enhancement is primarily attributed to the ability of the passivating ligand, STPD, to facilitate the charge-transfer process between the QCdSe and the triphenyldiamine (TPD) charge-transport matrix. The PR composites exhibited a maximum photocharge-generation efficiency of 0.9% and two-beam coupling gain coefficient of 110 cm-1. These figures of merit represent a significant improvement over similar composites photosensitized with more conventional trioctylphosphine oxide-passivated QCdSe (TQCdSe). Moreover, composites photosensitized with SQCdSe had a faster response time of τ = 128 ms at an electric field of 60 V/μm compared with τ = 982 ms for those containing TQCdSe. Because of the molecular similarity between the STPD passivating groups and the TPD-based charge-transport matrix, concentrations of up to 1.4 wt% of SQCdSe are achieved in PR composites without any detectable phase separation, a considerable improvement over the 0.7 wt% for TQCdSe.

  17. Investigation of reflectance gratings in PVK-based photorefractive polymers by photo-EMF and self-diffraction techniques

    NASA Astrophysics Data System (ADS)

    Stepanov, Serguei I.; Ramos-Garcia, Ruben; Camacho-Pernas, V.; Mansurova, Svetlana; Bittner, Reinhard; Meerholz, Klaus

    2002-01-01

    We report on simultaneous characterization of space charge gratings in photorefractive PVK-based polymer films by means of photo-EMF and Two-Wave Mixing (TWM) of periodically phase modulated beams. 100 micron thick samples of a polymer DMNPAA:PVK:ECZ:TNF with chromophore (DMNPAA) concentration of 5 wt% were investigated at (lambda) equals 633 nm in reflectance configuration. The amplitudes of the unshifted (i.e. drift induced) and the shifted (i.e. diffusion or saturation induced) components of the photorefractive space- charge field grating were evaluated directly by detection of the fundamental and the second harmonic of the TWM signal and indirectly from the corresponding harmonics of the photo-EMF current. The unshifted grating component exhibited approximately linear dependence on the externally applied dc field E0 and had an amplitude close to E0, which can be interpreted as absence of any remarkable saturation of trapping centers associated with photorefractive recording. Also growing with E0, the amplitude of the shifted component did not depend on the applied field direction, but was nearly as big as the unshifted component for the external fields of about approximately equals 50 V/micrometers . We interpret these facts as well as an experimentally observed double change of sign fo the fundamental harmonic photo-EMF signal with the external field as a result of dramatic growth of the Einstein ratio D/(mu) (relating diffusion coefficient D and mobility (mu) of the photogenerated carriers) - at least up to 1 V for the external dc field mentioned above. This allows us to address the observed shifted component as an external field enhanced diffusion grating, rather than the result of trapping centers saturation. Additionally, the (mu) (tau) product for dominating photocarriers (holes) was evaluated as approximately equals 0.3*10- 10 cm2/V from the photo-EMF measurements.

  18. Diffraction properties of transmission photorefractive volume gratings in a cerium-doped potassium sodium strontium barium niobate crystal.

    PubMed

    Liang, B L; Wang, Z Q; Mu, G G; Guan, J H; Cartwright, C M

    1999-09-10

    The diffraction efficiency of volume gratings written by two-wave mixing in a cerium-doped potassium sodium strontium barium niobate (Ce:KNSBN) photorefractive crystal is studied. It is found that the diffraction efficiency strongly depends on the polarization of writing beams and exhibits loop behavior with respect to the fringe modulation. The fringe modulations before and behind the crystal are compared. Modified coupled-wave theory is used to fit the experimental data. This research presents data that are relevant to the application of Ce:KNSBN crystals to holographic recording and optical information processing.

  19. Mutual transformation of light waves by reflection holograms in photorefractive crystals of the 4-bar 3m symmetry

    SciTech Connect

    Naunyka, V. N.; Shepelevich, V. V.

    2011-05-15

    The mutual transformation of light waves in the case of their simultaneous diffraction from a bulk reflection phase hologram, which was formed in a cubic photorefractive crystal of the 4-bar 3m symmetry class, has been studied. The indicator surfaces of the polarization-optimized values of the relative intensity of the object wave, which make it possible to determine the amplification of this wave for any crystal cut, are constructed. The linear polarization azimuths at which the energy exchange between the light waves reaches a maximum are found numerically for crystals of different cuts.

  20. Image correlation using isotropic and anisotropic higher-order generation and mutually pumped phase conjugation in photorefractive barium titanate

    NASA Astrophysics Data System (ADS)

    Buranasiri, Prathan; Banerjee, Partha P.; Polejaev, Vladimir; Sun, Ching-Cherng

    2003-10-01

    Using two beam coupling geometry, high order copropagating and contrapropagating isotropic and copropagating anisotropic self-diffraction are demonstrated using photorefractive cerium doped barium titanate. At small incident angles, typically less than 0.015 radians, both codirectional isotropic self-diffraction (CODIS) and contradirectional isotropic self-diffraction (CONDIS) orders are generated simultaneously. At larger incident angles, typically approximately more than 0.2094 radians, only codirectional anisotropic-self diffraction (CODAS) orders are generated. Ongoing work on image auto/cross correlation results are also shown.

  1. Laser Ultrasonic Thickness Measurements of Very Thick Walls at High Temperatures

    SciTech Connect

    Kruger, S. E.; Lord, M.; Monchalin, J.-P.

    2006-03-06

    Laser-ultrasonics presents many advantages compared to conventional ultrasonics, but is, generally, considered as less sensitive. As a consequence, laser-ultrasonics should not be adequate for ultrasonic measurements in coarse microstructure materials or measurements of large thicknesses. However, since the generated waves extend to very low frequencies, measurements in such conditions can be successfully performed if a photorefractive interferometer sensitive also to these low frequencies and properly balanced is used for detection. This is demonstrated by measurements of thicknesses up to 100 mm (4'') for various steel grades and at temperatures up to 1250 deg. C.

  2. Excimer laser treatment of corneal surface pathology: a laboratory and clinical study.

    PubMed Central

    Gartry, D.; Kerr Muir, M.; Marshall, J.

    1991-01-01

    The argon fluoride excimer laser emits radiation in the far ultraviolet part of the electromagnetic spectrum (193 nm). Each photon has high individual energy. Exposure of materials or tissues with peak absorption around 193 nm results in removal of surface layers (photoablation) with extremely high precision and minimal damage to non-irradiated areas. This precision is confirmed in a series of experiments on cadaver eyes and the treatment of 25 eyes with anterior corneal disease (follow-up 6 to 30 months). Multiple zone excimer laser superficial keratectomy is considered the treatment of choice for rough, painful corneal surfaces. All patients in this group were pain-free postoperatively. Where good visual potential exists, ablation of a single axial zone is recommended and results in improved visual acuity and reduction of glare. A hyperopic shift was noted in this group. Images PMID:1817467

  3. INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Action of the 216-nm fifth harmonic of a Nd:YAP laser on photosensitive germanosilicate glass films

    NASA Astrophysics Data System (ADS)

    Murav'ev, S. V.; Mal'shakova, O. A.; Golant, K. M.; Denisov, A. N.; Mashinsky, V. M.; Sazhin, O. D.

    2003-11-01

    The absorption spectrum, refractive index, and relief of the surface of a germanosilicate glass film are studied upon the non-destructive action of the 216-nm (5.75-eV) fifth harmonic of a repetitively pulsed Nd:YAP laser. It is shown that laser irradiation of films induces a strong photorefractive effect despite the relatively low absorption coefficient. For the 100-mJ cm-2 energy density and above, two-photon process make a noticeable contribution to the absorption of laser radiation at 216 nm. The diffraction efficiency of photoinduced phase gratings achieved ~7×10-3 for the exposure dose ~6 kJ cm-2, which corresponds to the induced refractive index 1.5×10-3. At higher exposure doses, a relief appears on a film surface and the diffraction efficiency of a phase grating is reduced.

  4. Laser-spectroscopy characterization of materials for frequency-agile solid-state laser systems. Final report, 15 Jan 88-14 Jan 91

    SciTech Connect

    Powell, R.C.

    1991-03-15

    This research involves the use of laser spectroscopy techniques to investigate materials which include laser crystals such as Cr{sup 3+}-doped alexandrite, emerald, garnets, and glass ceramics as well as Nd{sup 3+}-doped garnets and germinates and Ho{sup 3+}-doped fluorides. In addition, photorefractive processes were studied in potassium niobate crystals and in rare earth doped glasses. Some of the results of major importance from this work are: (1) The characterization of the properties of laser-induced gratings in glasses; (2) The elucidation of the effects of dopant ions on the photorefractive response of potassium niobate; (3) The observation of a new type of picosecond nonlinear optical response in potassium niobate associated with scattering from a Nb hopping mode; (4) The characterization of the properties of energy migration and radiationless relaxation processes in Cr{sup 3+} doped laser crystals; (5) The characterization of the pumping dynamics and lasing properties of Ho{sup 3+} in BaYb{sub 2}F{sub 8}; and (6) The characterization of the pumping dynamics and lasing properties of several Nd{sup 3+}-doped crystals.

  5. Charge carrier photogeneration, trapping, and space-charge field formation in PVK-based photorefractive materials

    NASA Astrophysics Data System (ADS)

    Däubler, T. K.; Bittner, R.; Meerholz, K.; Cimrová, V.; Neher, D.

    2000-05-01

    We studied the dark conductivity (jdark), the photoconductivity (jphoto), and the charge carrier photogeneration efficiency η of poly(N-vinylcarbazole)-based photorefractive (PR) materials with different glass-transition temperatures (Tg) and chromophore content (ρCHR). Measurements were carried out at wavelengths similar to those used in degenerate four-wave mixing (DFWM) and two-beam coupling (2BC) experiments. Both thick (37 μm) and thin samples (~1 μm) were analyzed. Photoconductivity experiments at different temperatures show that both jdark and jphoto are thermally activated. For jdark the activation is not related to the glass-transition temperature of the blends, whereas photocurrents exhibit a universal behavior with respect to Tr=Tg-T. The charge carrier photogeneration efficiency η was measured by xerographic discharge experiments. η was found to be independent of both Tg and of ρCHR. The photoconductivity gain factor G defined as the number of charge carriers measured in photoconductivity in relation to the number of carriers initially photogenerated as determined by the xerographic experiments is used to compare the results of photoconductivity and xerographic discharge experiments. G is found to be much smaller than unity even for thin samples, which indicates that the mean free path of the photogenerated charge carriers is less than 1 μm at photoelectrical equilibrium. Using Schildkraut's model for the space-charge field formation in organic PR materials, trap densities Ti of approximately 1017 cm-3 could be derived from G. The field and temperature dependence of Ti is independent of ρCHR and might account for the universal Tr dependence of jphoto. The estimated trap densities are used to calculate the first-order Fourier component of the space-charge field in the PR materials illuminated with a sinusoidal intensity pattern. Modifying Schildkraut's model so that the tilt between the applied electric field and the index of refraction grating

  6. Spectroscopic investigation of materials for frequency-agile laser systems. Final report, 15 January 1982-14 January 1985

    SciTech Connect

    Powell, R.C.

    1985-01-01

    This research involves the use of laser-spectroscopy techniques such as four-wave mixing, multiphoton absorption, time-resolved site-selection spectroscopy, and holography to characterize dynamical optical processes such as energy transfer, exciton migration, radiation-less relaxation, and the photorefractive effect. In addition, a significant effort was spent in the synthesis and characterization of new types of materials for tunable laser applications. The materials investigated include alexandrite, titanium-doped sapphire, lithium niobate, neodymium pentaphosphate, rhodium-doped rubidium calcium fluoride, manganese silicate, and neodymium-doped garnet crystals and glasses.

  7. Acousto-optical imaging using a powerful long pulse laser

    NASA Astrophysics Data System (ADS)

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

    2008-06-01

    Acousto-optical imaging is an emerging biodiagnostic technique which provides an optical spectroscopic signature and a spatial localization of an optically absorbing target 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. Although very promising for medical diagnostic, the practical application of this technique is presently limited by its poor sensitivity. Moreover, any method to enhance the signal-to-noise ratio must obviously satisfy the in vivo safety limits regarding the acceptable power level of both the ultrasonic pressure wave and the laser beam. In this paper, we propose to improve the sensitivity by using 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 also allows illuminating the tissues mainly during the transit time of the ultrasonic wave to maintain the average optical power below the maximum permissible exposure. In our experiment, a single-frequency Nd:YAG laser emitting 500-μs pulses with a peak power superior to 100 W was used. Photons were tagged in few-cm thick optical phantoms with tone bursts generated by an ultrasonic transducer. Tagged photons were detected with a GaAs photorefractive interferometer characterized by a large optical etendue to process simultaneously a large number of speckle grains. When pumped by high intensity laser pulses, such an interferometer also provides the fast response time essential to obtain an apparatus insensitive to the speckle decorrelation due to mechanical vibrations or tissues movements. The use of a powerful long pulse laser appears promising to enhance the signal level in ultrasound modulated optical imaging. When combined with a photorefractive interferometer of large optical etendue, such a source could

  8. Laser Materials and Laser Spectroscopy - A Satellite Meeting of IQEC '88

    NASA Astrophysics Data System (ADS)

    Wang, Zhijiang; Zhang, Zhiming

    1989-03-01

    * Mixing Frequency Generation of 271.0 - 291.5 nm in β - BaB2O4 * Low Temperature Absorption Steps Near Ultraviolet Intrinsic Edge in Beta Barium Metaborate * The Growth and Properties of BaTiO3 Crystals * High-order Phenomena Accompanied with Self-pumped Phase Conjugation in BaTiO * Growth and Laser Damage Estimation of Potassium Dihydrogen Phosphate Crystals for Laser Fusion * Noncritically Phase-matched KTP for Diode-pumped Lasers (400-700 nm) * Potassium Titanyl Phosphate (KTP): Properties and New Applications * A Kind of New Defect in KTP Crystal and its SHG Enhanced Effect * Nucleation and Growth of the Non-linear Optical Crystal Potassium Pentaborate Tetrahydrate * Quasi-periodic Oscillations in Photoinduced Conical Light Scattering from LiNbO3 : Fe Crystals * Laser Excited Photoreflectance of GaxIn1-xAs/InP Multiple Quantum Wells * Growth, Spectroscopic Properties and Applications of Doped LiNbO3 Crystals * Photorefractive and Photovoltaic Effect in Doped LiNbO3 * Recent Advances in Photorefractive Nonlinear Optics * Study on the Doubling-frequency and Anti-photorefractive Property of Heavily Magnesium-doped Lithium-rich Lithium Niobate Crystals * A New Technique for Increasing Two-wave Mixing Gain in Photorefractive Bi12SiO20 Crystals * Experimental Proof: There Existing Another Mechanism of Photorefractive Index in Crystal Ce-SBN * Effect of Crystal Annealing on Holographic Recording in Bismuth Silicon Oxide * Two Wave Coupling in KNbO3 Photorefractive Crystal * Photorefractive Effects in Nd-Doped Ferroelectric (KxNa1-x)0.4-(SryBa1-y)0.8 Nb2O6 Single Crystal * High Pressure Raman Spectra and the Effect of Pressure to the Ferroelastic Phase Transition in LnP5O15 * Time-delay Four-wave Mixing with Incoherent Light in Absorption Bands Treated as a Multi-level System * Pulsed Laser Induced Dislocation Structure in Lithium Fluoride Single Crystals * Laser Spectroscopy * Nonclassical Radiation from Single-atom Oscillators * Laser Spectroscopic Studies of Molecules in

  9. Time Measurement of Local Photorefractive Response of a Medium Using the π Shift of an Interference Pattern

    NASA Astrophysics Data System (ADS)

    Kozhevnikov, N. M.

    2016-03-01

    A method for the measurement of the recording/erasing time of dynamic phase gratings that are recorded by phase-modulated beams in photorefractive medium with local response is presented. The method is based on the detection of the intensity modulation of output beams in the course of rerecording of the grating after a shift of the interference pattern by one-half of spatial period. It is demonstrated that a relatively high sensitivity of the method is due to the selective detection of signals at a high frequency and a high efficiency of energy exchange of the recording beams in comparison with the diffraction of the probe beam. The application of the method in dynamic holographic seismographs is discussed.

  10. Self-deflection suppression of bright spatial solitons in absorbing photovoltaic photorefractive crystals by periodic diffusion management

    NASA Astrophysics Data System (ADS)

    Zheng, Cheng-Zhang; Luo, Man-Qiao; Lin, Guang; Cui, Hu; Luo, Ai-Ping

    2017-03-01

    The propagation behavior of bright spatial solitons under the diffusion effect in photovoltaic (PV) photorefractive (PR) crystals poled periodically is investigated by considering the optical absorption of the crystals. The numerical simulations show that, soliton beams follow a wiggling trajectory under the combined influence of the crystal absorption and the diffusion effect which is properly managed by designing the periodic domain inversion structure of periodically poled PV PR crystals. Moreover, the oscillation amplitude of the wiggling trajectory of a low-intensity soliton decreases gradually with the propagation distance, but the situation for a high-intensity soliton is contrary. Furthermore, the recursive equations describing the propagation trajectory are formulated and the analytical result of the propagation trajectory is in good agreement with the numerical one. The research results contribute to enriching the dynamics of PR spatial solitons and provide a method to suppress the self-deflection of soliton beams arising from the diffusion effect.

  11. Holographic recording and characterization of photorefractive Bi{sub 2}TeO{sub 5} crystals at 633 nm wavelength light

    SciTech Connect

    Oliveira, Ivan de

    2014-04-28

    We report on the holographic recording on photorefractive Bi{sub 2}TeO{sub 5} crystals using λ=633 nm wavelength light. We studied the behavior of this material under the action of this low photonic energy light and found out the presence of a fast and a slow hologram, both of photorefractive nature and exhibiting rather high diffraction efficiencies. The faster and the slower holograms are based on the excitation and diffusion of oppositely charged carriers (likely electrons and holes). Relevant parameters for the photoactive centers responsible for both kind of holograms were characterized using purely holographic techniques. No evidences of non-photosensitive ionic charge carriers being involved in the recording process at room temperature nor self-fixing effects were found.

  12. Two-wave mixing of ion-implanted photorefractive waveguides in near-stoichiometric Fe:LiNbO 3 crystals

    NASA Astrophysics Data System (ADS)

    Peng, Baogang; Chen, Feng; Tan, Yang; Kip, Detlef

    2011-04-01

    We report on the two-wave mixing of light in photorefractive waveguides in H ion-implanted Fe-doped near-stoichiometric lithium niobate crystals. For pump light of 632.8 nm wavelength a gain coefficient as high as 15 cm -1 is found. A response time of the order of a few seconds is achieved for micro-watt input powers.

  13. A multiplexed two-wave mixing interferometer for laser ultrasonic measurements of material anisotropy

    NASA Astrophysics Data System (ADS)

    Zhou, Yi; Murray, Todd W.; Krishnaswamy, Sridhar

    2002-05-01

    A method to optically measure ultrasonic displacements simultaneously over an array of detection points has been developed. Optical phase gratings are used to create a detection-array of laser beams that are directed to the specimen. The detection array can be arranged in several ways on the test object. The scattered beams from the detection-array are collected and combined with a single reference beam in a photorefractive crystal to from a multiplexed two-wave mixing (MTWM) configuration. Each of the output beams from the photorefractive crystal is imaged on to a separate element of a photodetector array. The resulting MTWM system is capable of providing simultaneous optical detection (with high spatial resolution and sub-nanometer displacement sensitivities) at several points on a test object. The MTWM system can be used in several modes for laser ultrasonic NDE of flaws and materials characterization. In this paper, the MTWM is used to characterize material anisotropy. Surface acoustic waves (SAWs) are generated using a pulsed laser focused to a point on a test object. The resulting SAW propagation is monitored optically simultaneously at 8 points arranged circularly around the generating spot. The scattered beams from the eight detection points are processed simultaneously in the MTWM setup. The group velocity slowness curve is obtained directly from the measured signals from the MTWM array. Results are shown for silicon and quartz. It is shown that the MTWM enables rapid experimental determination of material anisotropy.

  14. Growth and photorefractive properties of Mg, Fe co-doped near-stoichiometric lithium tantalate single crystals

    NASA Astrophysics Data System (ADS)

    Hsu, W. T.; Chen, Z. B.; You, C. A.; Huang, S. W.; Liu, J. P.; Lan, C. W.

    2010-07-01

    Mg, Fe co-doped near-stoichiometric lithium tantalate (SLT) crystals were successfully grown by the zone-leveling Czochralski (ZLCz) technique and the holographic properties were measured by the two-beam coupling method. The fundamental optical properties of crystals were measured by employing the UV-vis-NIR spectrometer and Fourier transformation infrared spectrophotometer as well. By the chemical analysis, the Li/Ta, Mg/Ta and Fe/Ta ratios of the crystals were obtained and the Li/Ta ratios of the crystals were all close to the theoretical limitation of 0.98. In the holographic properties, the recording time constant, erasing time constant, dynamic range, and sensitivity decreased with light intensity; but the maximum diffraction efficiency showed an opposite trend. Furthermore, the diffraction efficiency, dynamic range and sensitivity of the crystals were improved with a relatively higher Fe/Ta ratio. In comparison with Mn-LT crystals, the Mg, Fe co-doped SLT crystal showed the superior photorefractive properties indicating that it could be a promising new material for lifetime holographic data storage.

  15. Variation of doping-dependent properties in photorefractive SrxBa1-xNb2O6 : Ce, Cr, Ce+Cr

    NASA Astrophysics Data System (ADS)

    Kapphan, S.; Pedko, B.; Trepakov, V.; Savinov, M.; Pankrath, R.; Kislova, I.

    In congruent SrxBa1-xNb2O6 (SBN, x =0.61) the photorefractive properties are significantly enhanced by doping with Ce or Cr. The visible and FIR absorption increases linearly with the dopand concentration up to about 10,000 ppm (p.f.u.) of Ce or Cr or in double doped crystals (Ce+Cr). Simultaneously a decrease of the phase transition temperature T-c from about 253 K in pure SBN to about room temperature for doping concentrations (of Ce, Cr or both) of about 20,000 ppm (p.f.u.) is found.

  16. Coupled electric fields in photorefractive driven liquid crystal hybrid cells - theory and numerical simulation

    NASA Astrophysics Data System (ADS)

    Moszczyński, P.; Walczak, A.; Marciniak, P.

    2016-12-01

    In cyclic articles previously published we described and analysed self-organized light fibres inside a liquid crystalline (LC) cell contained photosensitive polymer (PP) layer. Such asymmetric LC cell we call a hybrid LC cell. Light fibre arises along a laser beam path directed in plane of an LC cell. It means that a laser beam is parallel to photosensitive layer. We observed the asymmetric LC cell response on an external driving field polarization. Observation has been done for an AC field first. It is the reason we decided to carry out a detailed research for a DC driving field to obtain an LC cell response step by step. The properly prepared LC cell has been built with an isolating layer and garbage ions deletion. We proved by means of a physical model, as well as a numerical simulation that LC asymmetric response strongly depends on junction barriers between PP and LC layers. New parametric model for a junction barrier on PP/LC boundary has been proposed. Such model is very useful because of lack of proper conductivity and charge carriers of band structure data on LC material.

  17. Holographic Reflection Filters in Photorefractive LiNbO3 Channel Waveguides

    NASA Astrophysics Data System (ADS)

    Kip, Detlef; Hukriede, Joerg

    Permanent refractive-index gratings in waveguide devices are of considerable interest for optical communication systems that make use of the high spectral selectivity of holographic filters, e.g. dense wavelength division multiplexing (DWDM) or narrow-bandwidth mirrors for integrated waveguide lasers in LiNbO3. Other possible applications include grating couplers and optical sensors. In this contribution we investigate such holographic wavelength filters in Fe- and Cu-doped LiNbO3 channel waveguides. Permanent refractive-index gratings are generated by thermal fixing of holograms in the waveguides. The samples are fabricated by successive in-diffusion of Ti stripes and thin layers of either Fe or Cu. After high-temperature recording with green light, refractive-index changes up to δ, ~10^-4 for infrared light ( 1.55,m) are obtained, resulting in a reflection efficiency well above 99% for a 15 mm-long grating. Several gratings for different wavelengths can be superimposed in the same sample, which may enable the fabrication of more complex filters, laser mirrors or optical sensors. By changing the sample temperature the reflection wavelength can be tuned by thermal expansion of the grating, and wavelength filters can be switched on and off by applying moderate voltages using the electro-optic effect. Furthermore, we report on a new thermal fixing mechanism that does not need any additional development by homogeneous light illumination and therefore does not suffer from the non-vanishing dark conductivity of the material.

  18. Self-scanning of a continuous-wave dye laser having a phase-conjugating resonator cavity.

    PubMed

    Feinberg, J; Bacher, G D

    1984-09-01

    A continuous-wave dye laser having a self-pumped phase conjugator in place of its usual output mirror will slowly change its own output wavelength with time. The laser has a bandwidth of 1.5 GHz and can self-scan to either longer or shorter wavelengths over a 37-nm range. The phase conjugator uses self-pumped four-wave mixing in a BaTiO(3) crystal. A ring laser that uses two-wave mixing in the same crystal is also observed to have a frequency offset of a few hertz compared with the frequency of the pumping beam. These two effects are related; both are caused by a spontaneously moving photorefractive-index grating in the BaTiO(3) crystal.

  19. Imaging Anisotropic Elastic Properties of an Orthotropic Paper Sheet Using Photorefractive Dynamic Holography

    SciTech Connect

    Telschow, Kenneth Louis; Deason, Vance Albert

    2002-12-01

    An important material property in the paper industry is the anisotropic stiffness distribution due to the fibrous microstructure of paper and to processing procedures. Ultrasonic methods offer a means of determining the stiffness of sheets of paper from the anisotropic propagation characteristics of elastic Lamb waves along the machine direction and the cross direction. That is, along and perpendicular to the direction of paper production. Currently, piezoelectric ultrasonic methods are employed in the industry to measure the elastic polar diagram of paper through multiple contacting measurements made in all directions. This paper describes a new approach utilizing the INEEL Laser Ultrasonic Camera to provide a complete image of the elastic waves traveling in all directions in the plane of the paper sheet. This approach is based on optical dynamic holographic methods that record the out of plane ultrasonic motion over the entire paper surface simultaneously without scanning. The full-field imaging technique offers great potential for increasing the speed of the measurement and it ultimately provides a substantial amount of information concerning local property variations and flaws in the paper. This report shows the success of the method and the manner in which it yields the elastic polar diagram for the paper from the dispersive flexural or antisymmetric Lamb wave.

  20. Laser irradiation, ion implantation, and e-beam writing of integrated optical structures

    NASA Astrophysics Data System (ADS)

    Righini, Giancarlo C.; Banyasz, I.; Berneschi, S.; Brenci, M.; Chiasera, A.; Cremona, M.; Ehrt, D.; Ferrari, M.; Montereali, R. M.; Nunzi Conti, G.; Pelli, S.; Sebastiani, S.; Tosello, C.

    2005-07-01

    Much attention is currently being paid to the materials and processes that allow one to directly write or to imprint waveguiding structures and/or diffractive elements for optical integrated circuits by exposure from a source of photons, electrons or ions. Here a brief overview of the results achieved in our laboratories is presented, concerning the fabrication and characterization of optical guiding structures based on different materials and exposure techniques. These approaches include: electron and ion beam writing of waveguides in (poly)-crystalline lithium fluoride, uv-laser printing of waveguides and gratings in photorefractive glass thin films, and fs-laser writing in tellurite glasses. Properties and perspectives of these approaches are also discussed.

  1. Photosensitivity of pulsed laser deposited Ge{sub 20}As{sub 20}Se{sub 60} and Ge{sub 10}As{sub 30}Se{sub 60} amorphous thin films

    SciTech Connect

    Hawlová, P.; Olivier, M.; Verger, F.; Nazabal, V.; Němec, P.

    2013-10-15

    Graphical abstract: - Highlights: • Amorphous Ge{sub 20}As{sub 20}Se{sub 60}/Ge{sub 10}As{sub 30}Se{sub 60} films are fabricated by pulsed laser deposition. • Photosensitivity of the layers is studied by employing spectroscopic ellipsometry. • As-deposited/relaxed thin films were irradiated by 593, 635, and 660 nm lasers. • Ge{sub 20}As{sub 20}Se{sub 60} layers present almost zero photorefraction in relaxed state. - Abstract: Amorphous Ge{sub 20}As{sub 20}Se{sub 60} and Ge{sub 10}As{sub 30}Se{sub 60} thin films are fabricated by pulsed laser deposition. Prepared films are characterized in terms of their morphology, chemical composition, and optical properties. Special attention is given to the photosensitivity of the layers, which was studied by spectroscopic ellipsometry with as-deposited, annealed and exposed films by three different laser sources (593, 635, and 660 nm). The results show better photostability for Ge{sub 20}As{sub 20}Se{sub 60} thin films, where photoinduced change of optical band gap was found to be equal or less than 0.04 eV and these layers present almost zero photorefraction.

  2. Laser apparatus

    NASA Technical Reports Server (NTRS)

    Koepf, G. A. (Inventor)

    1979-01-01

    A laser apparatus having a pump laser device for producing pump laser energy upon being excited is disclosed. The pump laser device has a resonating cavity for oscillating and amplifying the pump laser energy. A source laser device is used for producing source laser energy upon being excited by the pump laser energy. The source laser device has a resonating cavity for oscillating and amplifying the source laser energy. The source laser's resonating cavity is coupled within a portion of the pump laser's resonating cavity.

  3. Aircrew Performance Cutting-Edge Tech: Emerging Human Performance Enhancement Technology Vision in Support of Operational Military Aviation Strategy

    DTIC Science & Technology

    2002-04-01

    Ongoing areas within the evaluation of photorefractive keratectomy include pressure chamber, centrifuge, contrast sensitivity, and NVG effects. In 1998...night/enhanced night vision’ and ‘Will Mission Oriented Protective Posture gear required for the nuclear, biological, and chemical warfare environment...the NBC threat. Currently, the only defense includes Mission Oriented Protective Posture (MOPP) gear and aircraft modifications of the

  4. Imaging Laser Ultrasonics Measurement of the Elastodynamic Properties of Paper

    SciTech Connect

    Telschow, Kenneth Louis; Deason, Vance Albert

    2001-10-01

    Many sheet and plate material industries (e.g. paper) desire knowledge of the anisotropic stiffness properties of their material to optimize the manufacturing process. A determination of the anisotropic elastic matrix would be very beneficial for determination of parameters, such as as microstructural texture, fiber or grain orientation and stiffness. The propagation of ultrasonic waves in plates is a method for determining the anisotropic elastic properties in a nondestructive manner. Laser ultrasonics offes a noncontacting means to implement these measurements in the workplace by employing pulsed or modulated light to excite symmetric and antisymmetric plate waves concurrent with optical interferometric detection. Measurements can then be performed along the machine and cross directions to obtain parameters that are used empirically for process monitoring. Recently, the INEEL has developed a full-field view laser based ultrasonic imaging method that allows simultaneous measurement of plate wave motion in all planar directions within a single image without scanning. The imaging measurements are based on dynamic holography using photorefractive materials for interferometric deteciton and are operated as normal video rates. Results from this laser based imaging approach are presented that record Lamb wave mode wavefronts in all planar directions from localized sources in a single image. Specific numerical predictions for flexural wave propagation in distinctly different types of paper accounting fully for orthotropic anisotropy are presented and compared with direct imaging measurements. Very good agreement with theoretical calculations is obtained for the lowest antisymmetric plate mode in all planar directions using paper properties independently determined by others.

  5. Optimized Photorefractive Barium Titanate

    DTIC Science & Technology

    1992-03-11

    potassium dihydrogen phosphate (KDP), 6 and barium sodium niobate Ba2 NaNbsO%1 ,7 were examined. Unfortu- nately, the high optical intensities required for...Phys. Lett., 15, 210 (1969) 14. J. J. Amodei. D. L. Staebler. and A. W. Stephens, "Holographic Storage in Doped Barium Sodium Niobate ". Appl. Phys...equipped with precise computer control of the pulling and rotation system. The cylindrical furnace was found to be susceptible to cracking due to

  6. Harmonic fundamental self-pulsations from a laser diode using phase-conjugate optical feedback

    NASA Astrophysics Data System (ADS)

    Wolfersberger, Delphine; Karsaklian dal Bosco, A.; Mercier, E.; Sciamanna, M.

    2014-05-01

    Thanks to the band-gap engineering of quantum confined semiconductor materials and the development of semiconductor-based saturable absorber mirrors, recent years have seen the development of compact and low-cost external-cavity laser diodes generating pulses at several tens of GHz. The physics of the bifurcation leading to selfpulsation leads however to an intrinsic limitation: the fundamental repetition rate is fixed to and limited by the externalcavity round-trip time. By contrast, we demonstrate here that an external-cavity diode laser may generate fundamental self-pulsating dynamics at harmonics of the external-cavity frequency, when a phase conjugate mirror replaces the conventional mirror. As is known from theory, a laser diode with phase conjugate external feedback supports a single stationary solution that bifurcates to self-pulsating dynamics of increasing frequency when increasing the amount of light reflected back to the laser diode. The self-pulsation frequency then increases in step of the external-cavity frequency as one increases the feedback strength. We provide here the first experimental evidence of such harmonic external-cavity fundamental self-pulsation. As a proof-of-concept, we generate experimentally a self-pulsating dynamics at twice and three times the fundamental external-cavity frequency using an edge-emitting laser with a self-pumped ring-cavity photorefractive phase conjugator. Numerical simulations also predict stable higher harmonics.

  7. Evaluation of the Efficacy of Excimer Laser Ablation of Cross-Linked Porcine Cornea

    PubMed Central

    Chen, Shihao; Li, Yini; Stojanovic, Aleksander; Zhang, Jia; Wang, Yibo; Wang, Qinmei; Seiler, Theo

    2012-01-01

    Background Combination of riboflavin/UVA cross-linking (CXL) and excimer laser ablation is a promising therapy for treating corneal ectasia. The cornea is strengthened by cross-linking, while the irregular astigmatism is reduced by laser ablation. This study aims to compare the efficacy of excimer laser ablation on porcine corneas with and without cross-linking. Methods and Findings The porcine cornea was de-epithelialized and treated with 0.1% riboflavin solution for 30 minutes. A half of the cornea was exposed to UVA-radiation for another 30 minutes while the controlled half of the cornea was protected from the UVA using a metal shield. Photo therapeutic keratectomy (PTK) was then performed on the central cornea. Corneal thickness of 5 paired locations on the horizontal line, ±0.5, ±1.0, ±1.5, ±2.0, and ±2.5 mm from the central spot, were measured using optical coherence tomography prior to and after PTK. The ablation depth was then determined by the corneal thickness. There was a 9% difference (P<0.001) in the overall ablation depth between the CXL-half corneas (158±22 µm) and the control-half corneas (174±26 µm). The ablation depths of all 5 correspondent locations on the CXL-half were significantly smaller (P<0.001). Conclusion The efficacy of the laser ablation seems to be lower in cross-linked cornea. Current ablation algorithms may need to be modified for cross-linked corneas. PMID:23056269

  8. Combined treatment with flap amputation, phototherapeutic keratectomy, and collagen crosslinking in severe intractable post-LASIK atypical mycobacterial infection with corneal melt.

    PubMed

    Kymionis, George D; Kankariya, Vardhaman P; Kontadakis, Georgios A

    2012-04-01

    A 23-year-old woman was referred for management of intractable post-laser in situ keratomileusis (LASIK) keratitis due to atypical mycobacteria in the left eye. Corrected distance visual acuity was 20/20 in the right eye and counting fingers at 3 meters in the left eye. Slitlamp examination revealed multiple infiltrates in the flap interface and severe corneal stromal melting with thinning. Despite maximum antibiotic therapy for 7 days, the keratitis continued to worsen. A penetrating keratoplasty (PKP) was scheduled. While waiting for a corneal graft, corneal collagen crosslinking (CXL) with riboflavin and ultraviolet-A was proposed as an alternative treatment. Flap amputation and limited phototherapeutic keratotomy (PTK) (10 μm) were also performed. One week postoperatively, all infiltrates and stromal edema had resolved. At 3 months, the uncorrected distance visual acuity improved to 20/35. Corneal crosslinking after flap amputation and limited PTK was an effective treatment for severe intractable post-LASIK keratitis with corneal melting and obviated PKP.

  9. Electrostatic modification of ZnSe/polymer interface in polymer-nematogen composite and its impact on photorefractive hologram

    NASA Astrophysics Data System (ADS)

    Zhang, Jingwen; Fu, Jiayin; Hu, Guangwei; Zhao, Hua

    2015-09-01

    With submicrometer thick photoconducting, semiconductor ZnSe thin films as interlayers between ITO glass and thin film of C60 doped mixture of polymer poly[N-vinylcarbazole] (PVK) and nematic liquid crystal (LC) 4,4'-npentylcyanobiphenyl (5CB), an updatable holographic recording medium was fabricated. When two laser beams were overlapped in the holographic recording medium, 2D diffraction patterns were seen, along with several interesting observations. The frequent sign changing of energy transferring between the two transmitted laser beams and large dynamic change in different diffraction orders implied complex processes of electric charge generation, transportation and compensation in the interfaces and within composite polymer film. Electrostatic modification based surface grating formation was proposed to explain all the findings.

  10. Laser clock

    SciTech Connect

    Facklam, R.L.

    1983-05-26

    A laser clock includes a linear laser in one embodiment of the clock and a ring laser gyro in the other embodiment. The linear laser is frequency stabilized and utilizes a single active medium in the form of a low pressure gas, such as He-Ne, with a Doppler broadened gain curve. The ring laser gyro is a four frequency laser with a Faraday rotor. Detector and electronic circuitry associated with the laser of each embodiment detects a beat frequency and convert it to a clock signal.

  11. Imaging the ultrafast Kerr effect, free carrier generation, relaxation and ablation dynamics of Lithium Niobate irradiated with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Garcia-Lechuga, Mario; Siegel, Jan; Hernandez-Rueda, Javier; Solis, Javier

    2014-09-01

    The interaction of high-power single 130 femtosecond (fs) laser pulses with the surface of Lithium Niobate is experimentally investigated in this work. The use of fs-resolution time-resolved microscopy allows us to separately observe the instantaneous optical Kerr effect induced by the pulse and the generation of a free electron plasma. The maximum electron density is reached 550 fs after the peak of the Kerr effect, confirming the presence of a delayed carrier generation mechanism. We have also observed the appearance of transient Newton rings during the ablation process, related to optical interference of the probe beam reflected at the front and back surface of the ablating layer. Finally, we have analyzed the dynamics of the photorefractive effect on a much longer time scale by measuring the evolution of the transmittance of the irradiated area for different fluences below the ablation threshold.

  12. Imaging the ultrafast Kerr effect, free carrier generation, relaxation and ablation dynamics of Lithium Niobate irradiated with femtosecond laser pulses

    SciTech Connect

    Garcia-Lechuga, Mario Siegel, Jan Hernandez-Rueda, Javier; Solis, Javier

    2014-09-21

    The interaction of high-power single 130 femtosecond (fs) laser pulses with the surface of Lithium Niobate is experimentally investigated in this work. The use of fs-resolution time-resolved microscopy allows us to separately observe the instantaneous optical Kerr effect induced by the pulse and the generation of a free electron plasma. The maximum electron density is reached 550 fs after the peak of the Kerr effect, confirming the presence of a delayed carrier generation mechanism. We have also observed the appearance of transient Newton rings during the ablation process, related to optical interference of the probe beam reflected at the front and back surface of the ablating layer. Finally, we have analyzed the dynamics of the photorefractive effect on a much longer time scale by measuring the evolution of the transmittance of the irradiated area for different fluences below the ablation threshold.

  13. Blue Laser.

    DTIC Science & Technology

    1985-12-01

    HOLLOW CATHODE LASER FABRICATION 13 4. EXPERIENCE WITH THE BLUE LASER 18 4.1 Operational and Processing Experience 18 4.2 Performance Testing 20 5...34 -. - . •. SECTION 3 BLUE HOLLOW CATHODE LASER FABRICATION This section presents an overview of the steps taken in creating a HCL. There is...to the laser assembly. These steps can actually be considered as the final steps in laser fabrication because some of them involve adding various

  14. Synthesis and functionalization of a triaryldiamine-base photoconductive/photorefractive composite, and its application to aberrated image restoration

    NASA Astrophysics Data System (ADS)

    Liang, Yichen

    Organic phoorefractive (PR) composites have recently emerged as an important class of materials for applications including high-density data storage, optical communication, and biomedical imaging. In an effort to further improve their performance, this study focused on the utilization of functionalized semiconductor nanocrystals to photosensitize triaryamine (TPD)-based PR composites, as well as the application of TPD-based PR composites in the restoration of aberrated optical information. A novel approach to functionalize CdSe quantum dot (QCdSe) was firstly introduced where the sulfonated triarydiamine (STPD) was used as charge-transporting ligand to passivate QCdSe. TPD-based photoconductive and PR composites were photosensitized with the STPD-passivated QCdSe (SQCdSe). Due to the charge-transporting capability of STPD, the composites photosensitized with STPD-capped QCdSe exhibited superior performance relative to composites employing more traditional photosensitizers (such as fullerene C60 and trioctylphosphine-capped QCdSe), with figures-of-merit including photoconductivities in excess of 60 pS/cm, two-beam coupling gain coefficients in excess of 110 cm-1, and PR response time of less than 30 ms. In addition, the ability of TPD-based PR composites to correct aberrations associated with a laser beam was described. Here, a severely aberrated laser beam was able to be restored to a nearly unaberrated condition through the PR process, and the potential of this technique for practical applications was well explained. Based on the current experimental geometry, a PR response time of 0.5 s was observed, which is the fastest PR response time reported for a PR composite operating under experimental conditions designed for the correction of optical aberrations.

  15. Lasers of All Sizes

    NASA Astrophysics Data System (ADS)

    Balcou, Philippe; Forget, Sébastien Robert-Philip, Isabelle

    2015-10-01

    * Introduction * The Laser in All Its Forms * Gas lasers * Dye lasers * Solid-state lasers * Lasers for Every Taste * The rise of lasers * Lasers of all sizes * The colors of the rainbow... and beyond * Shorter and shorter lasers * Increasingly powerful lasers * Lasers: A Universal Tool? * Cutting, welding, and cleaning * Communicating * Treating illnesses * Measuring * Supplying energy? * Entertaining * Understanding * Conclusion

  16. Laser microphone

    DOEpatents

    Veligdan, James T.

    2000-11-14

    A microphone for detecting sound pressure waves includes a laser resonator having a laser gain material aligned coaxially between a pair of first and second mirrors for producing a laser beam. A reference cell is disposed between the laser material and one of the mirrors for transmitting a reference portion of the laser beam between the mirrors. A sensing cell is disposed between the laser material and one of the mirrors, and is laterally displaced from the reference cell for transmitting a signal portion of the laser beam, with the sensing cell being open for receiving the sound waves. A photodetector is disposed in optical communication with the first mirror for receiving the laser beam, and produces an acoustic signal therefrom for the sound waves.

  17. Laser ignition

    DOEpatents

    Early, James W.; Lester, Charles S.

    2004-01-13

    Sequenced pulses of light from an excitation laser with at least two resonator cavities with separate output couplers are directed through a light modulator and a first polarzing analyzer. A portion of the light not rejected by the first polarizing analyzer is transported through a first optical fiber into a first ignitor laser rod in an ignitor laser. Another portion of the light is rejected by the first polarizing analyzer and directed through a halfwave plate into a second polarization analyzer. A first portion of the output of the second polarization analyzer passes through the second polarization analyzer to a second, oscillator, laser rod in the ignitor laser. A second portion of the output of the second polarization analyzer is redirected by the second polarization analyzer to a second optical fiber which delays the beam before the beam is combined with output of the first ignitor laser rod. Output of the second laser rod in the ignitor laser is directed into the first ignitor laser rod which was energized by light passing through the first polarizing analyzer. Combined output of the first ignitor laser rod and output of the second optical fiber is focused into a combustible fuel where the first short duration, high peak power pulse from the ignitor laser ignites the fuel and the second long duration, low peak power pulse directly from the excitation laser sustains the combustion.

  18. Laser sampling

    NASA Astrophysics Data System (ADS)

    Gorbatenko, A. A.; Revina, E. I.

    2015-10-01

    The review is devoted to the major advances in laser sampling. The advantages and drawbacks of the technique are considered. Specific features of combinations of laser sampling with various instrumental analytical methods, primarily inductively coupled plasma mass spectrometry, are discussed. Examples of practical implementation of hybrid methods involving laser sampling as well as corresponding analytical characteristics are presented. The bibliography includes 78 references.

  19. CW laser pumped emerald laser

    SciTech Connect

    Shand, M.L.; Lai, S.T.

    1984-02-01

    A CW laser-pumped emerald laser is reported. A 34 percent output power slope efficiency is observed with longitudinal pumping by a krypton laser in a nearly concentric cavity. The laser has been tuned from 728.8 to 809.0 nm. Losses in emerald are larger than those of alexandrite determined in a similar cavity. The present data also indicate that the excited state absorption minimum is shifted from that of alexandrite. 13 references.

  20. Connective tissue growth factor is not necessary for haze formation in excimer laser wounded mouse corneas

    PubMed Central

    Feng, Xiaodi; Pi, Liya; Sriram, Sriniwas; Schultz, Gregory S.

    2017-01-01

    We sought to determine if connective tissue growth factor (CTGF) is necessary for the formation of corneal haze after corneal injury. Mice with post-natal, tamoxifen-induced, knockout of CTGF were subjected to excimer laser phototherapeutic keratectomy (PTK) and the corneas were allowed to heal. The extent of scaring was observed in non-induced mice, heterozygotes, and full homozygous knockout mice and quantified by macrophotography. The eyes from these mice were collected after euthanization for re-genotyping to control for possible Cre-mosaicism. Primary corneal fibroblasts from CTGF knockout corneas were established in a gel plug assay. The plug was removed, simulating an injury, and the rate of hole closure and the capacity for these cells to form light reflecting cells in response to CTGF and platelet-derived growth factor B (PDGF-B) were tested and compared to wild-type cells. We found that independent of genotype, each group of mice was still capable of forming light reflecting haze in the cornea after laser ablation (p = 0.40). Results from the gel plug closure rate in primary cell cultures of knockout cells were not statistically different from serum starved wild-type cells, independent of treatment. Compared to the serum starved wild-type cells, stimulation with PDGF-BB significantly increased the KO cell culture’s light reflection (p = 0.03). Most interestingly, both reflective cultures were positive for α-SMA, but the cellular morphology and levels of α-SMA were distinct and not in proportion to the light reflection seen. This new work demonstrates that corneas without CTGF can still form sub-epithelial haze, and that the light reflecting phenotype can be reproduced in culture. These data support the possibilities of growth factor redundancy and that multiple pro-haze pathways exist. PMID:28207886

  1. Laser device

    DOEpatents

    Scott, Jill R.; Tremblay, Paul L.

    2007-07-10

    A laser device includes a target position, an optical component separated a distance J from the target position, and a laser energy source separated a distance H from the optical component, distance H being greater than distance J. A laser source manipulation mechanism exhibits a mechanical resolution of positioning the laser source. The mechanical resolution is less than a spatial resolution of laser energy at the target position as directed through the optical component. A vertical and a lateral index that intersect at an origin can be defined for the optical component. The manipulation mechanism can auto align laser aim through the origin during laser source motion. The laser source manipulation mechanism can include a mechanical index. The mechanical index can include a pivot point for laser source lateral motion and a reference point for laser source vertical motion. The target position can be located within an adverse environment including at least one of a high magnetic field, a vacuum system, a high pressure system, and a hazardous zone. The laser source and an electro-mechanical part of the manipulation mechanism can be located outside the adverse environment. The manipulation mechanism can include a Peaucellier linkage.

  2. Laser device

    DOEpatents

    Scott, Jill R.; Tremblay, Paul L.

    2004-11-23

    A laser device includes a target position, an optical component separated a distance J from the target position, and a laser energy source separated a distance H from the optical component, distance H being greater than distance J. A laser source manipulation mechanism exhibits a mechanical resolution of positioning the laser source. The mechanical resolution is less than a spatial resolution of laser energy at the target position as directed through the optical component. A vertical and a lateral index that intersect at an origin can be defined for the optical component. The manipulation mechanism can auto align laser aim through the origin during laser source motion. The laser source manipulation mechanism can include a mechanical index. The mechanical index can include a pivot point for laser source lateral motion and a reference point for laser source vertical motion. The target position can be located within an adverse environment including at least one of a high magnetic field, a vacuum system, a high pressure system, and a hazardous zone. The laser source and an electro-mechanical part of the manipulation mechanism can be located outside the adverse environment. The manipulation mechanism can include a Peaucellier linkage.

  3. Laser ignition

    DOEpatents

    Early, James W.; Lester, Charles S.

    2003-01-01

    In the apparatus of the invention, a first excitation laser or other excitation light source is used in tandem with an ignitor laser to provide a compact, durable, engine deployable fuel ignition laser system. Reliable fuel ignition is provided over a wide range of fuel conditions by using a single remote excitation light source for one or more small lasers located proximate to one or more fuel combustion zones. In a third embodiment, alternating short and long pulses of light from the excitation light source are directed into the ignitor laser. Each of the embodiments of the invention can be multiplexed so as to provide laser light energy sequentially to more than one ignitor laser.

  4. [Does refractive surgery really make eyeglasses superfluous?].

    PubMed

    Seiler, T

    2001-06-14

    Spectacles have become a problem of life-style in some societies. In the USA, in 1999 approximately 1 million LASIK operations have been performed to correct myopia and astigmatism and in Europe the frequency of refractive surgery stead by increases. However, only 3 to 5% of these operations are medically indicated. Refractive surgery is evaluated regarding safety and efficacy. Modern laser techniques demonstrate excellent refractive results: photorefractive keratectomy (PRK) achieved refractive success rates of 90% and more with complication rates of 0.5% and less. PRK is, therefore, a valuable technique for corrections of myopia up to -6.0 D. Similar efficacy is obtained with LASIK (laser in situ keratomileusis) in corrections up to -10 D, however, the complication rate is somewhat higher. Laser correction of hyperopia is equally successful regarding the refractive success but shows an even higher complication rate and the patient satisfaction is lower. Modern refractive laser surgery may replace spectacles in the majority of the cases, however, none of the techniques is free of complications. Therefore, we understand refractive surgery still to be inferior to the correction of ametropia by means of spectacles and any such operation should be attempted only after thorough discussion.

  5. One — dimensional laser beam steering using frequency detuning in two — wave mixing with a BaTiO 3 crystal

    NASA Astrophysics Data System (ADS)

    Dharmsaktu, K. S.; Joseph, Joby; Singh, Kehar

    2000-06-01

    We demonstrate a method of one-dimensional laser beam deflection using frequency detuning in two-wave mixing. Energy exchange between the interfering beams in a photo-refractive BaTiO 3 crystal has been used for deflection of a pump beam into predetermined probe beam directions. A one-dimensional array of several beams is generated from a single probe beam, employing a piezo-mirror and beam splitter combination. Probe beams so produced are detuned by exciting the piezo-mirror with a periodic near-saw-tooth voltage so as to produce running fringes. However, stable holographic gratings are recorded by matching the frequency of the probe beam with that of a pump beam reflected from another vibrating piezo-mirror, thereby controlling the direction of beam deflection.

  6. Biocavity Lasers

    SciTech Connect

    Gourley, P.L.; Gourley, M.F.

    2000-10-05

    Laser technology has advanced dramatically and is an integral part of today's healthcare delivery system. Lasers are used in the laboratory analysis of human blood samples and serve as surgical tools that kill, burn or cut tissue. Recent semiconductor microtechnology has reduced the size o f a laser to the size of a biological cell or even a virus particle. By integrating these ultra small lasers with biological systems, it is possible to create micro-electrical mechanical systems that may revolutionize health care delivery.

  7. Laser apparatus

    DOEpatents

    Lewis, Owen; Stogran, Edmund M.

    1980-01-01

    Laser apparatus is described wherein an active laser element, such as the disc of a face-pumped laser, is mounted in a housing such that the weight of the element is supported by glass spheres which fill a chamber defined in the housing between the walls of the housing and the edges of the laser element. The uniform support provided by the spheres enable the chamber and the pump side of the laser element to be sealed without affecting the alignment or other optical properties of the laser element. Cooling fluid may be circulated through the sealed region by way of the interstices between the spheres. The spheres, and if desired also the cooling fluid may contain material which absorbs radiation at the wavelength of parasitic emissions from the laser element. These parasitic emissions enter the spheres through the interface along the edge surface of the laser element and it is desirable that the index of refraction of the spheres and cooling fluid be near the index of refraction of the laser element. Thus support, cooling, and parasitic suppression functions are all accomplished through the use of the arrangement.

  8. Laser ignition

    DOEpatents

    Early, James W.; Lester, Charles S.

    2002-01-01

    In the apparatus of the invention, a first excitation laser or other excitation light source capable of producing alternating beams of light having different wavelengths is used in tandem with one or more ignitor lasers to provide a compact, durable, engine deployable fuel ignition laser system. Reliable fuel ignition is provided over a wide range of fuel conditions by using the single remote excitation light source for pumping one or more small lasers located proximate to one or more fuel combustion zones with alternating wavelengths of light.

  9. Multimegajoule laser design. [Glass lasers

    SciTech Connect

    Manes, K.R.; Ozarski, R.G.; Hagen, W.F.; Holzrichtr, J.F.

    1985-08-01

    New technologies make multimegajoule glass lasers economically feasible. We have devised new laser architectures using harmonic switchout, target-plane holographic injection, phase conjugation, continuous apodization, and higher amplifier efficiencies. Our plan for building a multimegajoule laser for a recurring cost under $300 million relies on the following manufacturing economies of scale: high-volume glass production, rapid harmonic-crystal growth, capacitor sizing and packing to increase energy capacity, and part standardization.

  10. Heterodyne laser spectroscopy system

    DOEpatents

    Wyeth, Richard W.; Paisner, Jeffrey A.; Story, Thomas

    1989-01-01

    A heterodyne laser spectroscopy system utilizes laser heterodyne techniques for purposes of laser isotope separation spectroscopy, vapor diagnostics, processing of precise laser frequency offsets from a reference frequency and the like, and provides spectral analysis of a laser beam.

  11. Heterodyne laser spectroscopy system

    DOEpatents

    Wyeth, Richard W.; Paisner, Jeffrey A.; Story, Thomas

    1990-01-01

    A heterodyne laser spectroscopy system utilizes laser heterodyne techniques for purposes of laser isotope separation spectroscopy, vapor diagnostics, processing of precise laser frequency offsets from a reference frequency, and provides spectral analysis of a laser beam.

  12. Co Laser.

    DTIC Science & Technology

    1976-01-01

    newsletter setvice covering the moj-t recent research findings in 25 areas of industrial, technological , and sociological interest— invaluable information...service will be backdated to furnish you microfiche of reports issued earlier. Because of contractual arrangements with several Special Technology ...pressure electrical CO laser and, thereby, to develop the technology for high pres- sure, scalable, electric CO lasers exhibiting properties of

  13. Laser device

    DOEpatents

    Scott, Jill R.; Tremblay, Paul L.

    2008-08-19

    A laser device includes a virtual source configured to aim laser energy that originates from a true source. The virtual source has a vertical rotational axis during vertical motion of the virtual source and the vertical axis passes through an exit point from which the laser energy emanates independent of virtual source position. The emanating laser energy is collinear with an orientation line. The laser device includes a virtual source manipulation mechanism that positions the virtual source. The manipulation mechanism has a center of lateral pivot approximately coincident with a lateral index and a center of vertical pivot approximately coincident with a vertical index. The vertical index and lateral index intersect at an index origin. The virtual source and manipulation mechanism auto align the orientation line through the index origin during virtual source motion.

  14. High throughput laser processing

    SciTech Connect

    Harley, Gabriel; Pass, Thomas; Cousins, Peter John; Viatella, John

    2016-12-27

    A solar cell is formed using a solar cell ablation system. The ablation system includes a single laser source and several laser scanners. The laser scanners include a master laser scanner, with the rest of the laser scanners being slaved to the master laser scanner. A laser beam from the laser source is split into several laser beams, with the laser beams being scanned onto corresponding wafers using the laser scanners in accordance with one or more patterns. The laser beams may be scanned on the wafers using the same or different power levels of the laser source.

  15. Laser goniometer

    DOEpatents

    Fairer, George M.; Boernge, James M.; Harris, David W.; Campbell, DeWayne A.; Tuttle, Gene E.; McKeown, Mark H.; Beason, Steven C.

    1993-01-01

    The laser goniometer is an apparatus which permits an operator to sight along a geologic feature and orient a collimated lamer beam to match the attitude of the feature directly. The horizontal orientation (strike) and the angle from horizontal (dip), are detected by rotary incremental encoders attached to the laser goniometer which provide a digital readout of the azimuth and tilt of the collimated laser beam. A microprocessor then translates the square wave signal encoder outputs into an ASCII signal for use by data recording equipment.

  16. Laser propulsion

    NASA Technical Reports Server (NTRS)

    Rom, F. E.; Putre, H. A.

    1972-01-01

    The use of an earth-based high-power laser beam to provide energy for earth-launched rocket vehicle is investigated. The laser beam energy is absorbed in an opaque propellant gas and is converted to high-specific-impulse thrust by expanding the heated propellant to space by means of a nozzle. This laser propulsion scheme can produce specific impulses of several thousand seconds. Payload to gross-weight fractions about an order of magnitude higher than those for conventional chemical earth-launched vehicles appear possible. There is a potential for a significant reduction in cost per payload mass in earth orbit.

  17. Explosive laser

    DOEpatents

    Robinson, C.P.; Jensen, R.J.; Davis, W.C.; Sullivan, J.A.

    1975-09-01

    This patent relates to a laser system wherein reaction products from the detonation of a condensed explosive expand to form a gaseous medium with low translational temperature but high vibration population. Thermal pumping of the upper laser level and de-excitation of the lower laser level occur during the expansion, resulting in a population inversion. The expansion may be free or through a nozzle as in a gas-dynamic configuration. In one preferred embodiment, the explosive is such that its reaction products are CO$sub 2$ and other species that are beneficial or at least benign to CO$sub 2$ lasing. (auth)

  18. [Laser myringotomy].

    PubMed

    Hassmann-Poznańska, Elzbieta; Skotnicka, Bozena

    2002-01-01

    The aim of the study was assessment of the qualities of laser-assisted myringotomy (LAM) as a treatment for acute and secretory otitis media. Laser-assisted myringotomy was performed on 65 children (113 ears) mean age 6.2 years diagnosed with secretory otitis media (80%), recurrent secretory otitis media (11%) and acute otitis media (9%). Myringotomy was performed under general anesthesia using the OtoLAM device (ESC/Sharplan, Israel). In 64 ears pressure equalisation tubes were inserted after fenestration of the tympanic membrane with laser. Adenoidectomy alone or with tonsillectomy was performed at the same time in 51 cases. Laser tympanostomies remained patent for 7-32 days. All tympanostomies healed with no noticeable scarring. LAM appears to be a safe, and easy to performed, alternative technique in the treatment of otitis media.

  19. Laser fusion

    SciTech Connect

    Smit, W.A.; Boskma, P.

    1980-12-01

    Unrestricted laser fusion offers nations an opportunity to circumvent arms control agreements and develop thermonuclear weapons. Early laser weapons research sought a clean radiation-free bomb to replace the fission bomb, but this was deceptive because a fission bomb was needed to trigger the fusion reaction and additional radioactivity was induced by generating fast neutrons. As laser-implosion experiments focused on weapons physics, simulating weapons effects, and applications for new weapons, the military interest shifted from developing a laser-ignited hydrogen bomb to more sophisticated weapons and civilian applications for power generation. Civilian and military research now overlap, making it possible for several countries to continue weapons activities and permitting proliferation of nuclear weapons. These countries are reluctant to include inertial confinement fusion research in the Non-Proliferation Treaty. 16 references. (DCK)

  20. Laser barometer

    SciTech Connect

    Abercrombie, K.R.; Shiels, D.; Rash, T.

    1998-04-01

    This paper describes an invention of a pressure measuring instrument which uses laser radiation to sense the pressure in an enclosed environment by means of measuring the change in refractive index of a gas - which is pressure dependent.

  1. Laser Cutting

    DTIC Science & Technology

    1988-06-01

    lasers that are optically modified to produce high beam quality at reduced power levels for precision drilling and trepanning. * Nd:YAG lasers with...a smooth, dross-free cut face while the marking consists of a series of precisely placed shallow pits where surface finish and dross are not usually...neodymium:yttrium-aluminum-garnet (Nd:YAG) pulsed cutting data because the technique is considered vital in meeting the detailed precision cutting

  2. Laser Technology

    NASA Technical Reports Server (NTRS)

    1989-01-01

    Amoco Laser Company, a subsidiary of Amoco Corporation, has developed microlasers for the commercial market based on a JPL concept for optical communications over interplanetary distances. Lasers emit narrow, intense beams of light or other radiation. The beams transmit communication signals, drill, cut or melt materials or remove diseased body tissue. The microlasers cover a broad portion of the spectrum, and performance is improved significantly. Current applications include medical instrumentation, color separation equipment, telecommunications, etc.

  3. Applicability of supervised discriminant analysis models to analyze astigmatism clinical trial data

    PubMed Central

    Sedghipour, Mohammad Reza; Sadeghi-Bazargani, Homayoun

    2012-01-01

    Background In astigmatism clinical trials where more complex measurements are common, especially in nonrandomized small sized clinical trials, there is a demand for the development and application of newer statistical methods. Methods The source data belonged to a project on astigmatism treatment. Data were used regarding a total of 296 eyes undergoing different astigmatism treatment modalities: wavefront-guided photorefractive keratectomy, cross-cylinder photorefractive keratectomy, and monotoric (single) photorefractive keratectomy. Astigmatism analysis was primarily done using the Alpins method. Prior to fitting partial least squares regression discriminant analysis, a preliminary principal component analysis was done for data overview. Through fitting the partial least squares regression discriminant analysis statistical method, various model validity and predictability measures were assessed. Results The model found the patients treated by the wavefront method to be different from the two other treatments both in baseline and outcome measures. Also, the model found that patients treated with the cross-cylinder method versus the single method didn’t appear to be different from each other. This analysis provided an opportunity to compare the three methods while including a substantial number of baseline and outcome variables. Conclusion Partial least squares regression discriminant analysis had applicability for the statistical analysis of astigmatism clinical trials and it may be used as an adjunct or alternative analysis method in small sized clinical trials. PMID:23055670

  4. Laser Angioplasty

    NASA Technical Reports Server (NTRS)

    1990-01-01

    The principal method of dealing with coronary artery blockage is bypass surgery. A non-surgical alternative available to some patients is balloon angioplasty. For several years, medical researchers have been exploring another alternative that would help a wider circle of patients than the balloon treatment and entail less risk than bypass surgery. A research group is on the verge of an exciting development: laser angioplasty with a 'cool' type of laser, called an excimer laser, that does not damage blood vessel walls and offers non-surgical cleansing of clogged arteries with extraordinary precision. The system is the Dymer 200+ Excimer Laser Angioplasty System, developed by Advanced Intraventional Systems. Used in human clinical tests since 1987, the system is the first fully integrated 'cool' laser capable of generating the requisite laser energy and delivering the energy to target arteries. Thirteen research hospitals in the U.S. have purchased Dymer 200+ systems and used them in clinical trials in 121 peripheral and 555 coronary artery cases. The success rate in opening blocked coronary arteries is 85 percent, with fewer complications than in balloon angioplasty. Food and Drug Administration approval for the system is hoped for in the latter part of 1990. * Advanced Intraventional Systems became Spectranetics in 1994 and discontinued the product.

  5. Laser optomechanics

    PubMed Central

    Yang, Weijian; Adair Gerke, Stephen; Wei Ng, Kar; Rao, Yi; Chase, Christopher; Chang-Hasnain, Connie J.

    2015-01-01

    Cavity optomechanics explores the interaction between optical field and mechanical motion. So far, this interaction has relied on the detuning between a passive optical resonator and an external pump laser. Here, we report a new scheme with mutual coupling between a mechanical oscillator supporting the mirror of a laser and the optical field generated by the laser itself. The optically active cavity greatly enhances the light-matter energy transfer. In this work, we use an electrically-pumped vertical-cavity surface-emitting laser (VCSEL) with an ultra-light-weight (130 pg) high-contrast-grating (HCG) mirror, whose reflectivity spectrum is designed to facilitate strong optomechanical coupling, to demonstrate optomechanically-induced regenerative oscillation of the laser optomechanical cavity. We observe >550 nm self-oscillation amplitude of the micromechanical oscillator, two to three orders of magnitude larger than typical, and correspondingly a 23 nm laser wavelength sweep. In addition to its immediate applications as a high-speed wavelength-swept source, this scheme also offers a new approach for integrated on-chip sensors. PMID:26333804

  6. Searching for Better Photorefractive Materials

    DTIC Science & Technology

    2007-11-02

    monomers. It was found that the palladium mediated Stille coupling reaction is mild enough to tolerate the NLO chromophore and yielded polymers with...afford the NLO chromphores/monomers M1 and M2. As shown in Scheme 2, all the PR polymers were synthesized with high yields by palladium -catalyzed Stille...butyllithium but labile to fluoride -mediated cleavage.[ 6 1 Our synthetic strategy was to build TMSE-thio protecting group at the beginning, taking

  7. Photorefractive Polymer Fibers and Devices

    DTIC Science & Technology

    2008-10-31

    Emission and Recoverable Photodegradation in a Robust Dye -Doped Polymer," Proc. SPIE 4798, 60-68 (2002). 21. J. J. Park, S. Bian, and M. G. Kuzyk, "Dynamics...be possible to make arrays of RGB fibers so that full color perception is possible. We have been using the photoisomerization mechanisms in azo- dyes to...azo- dye -doped polymer. The resulting decrease in the refractive index yields beam spreading. Beam defocusing in DRI/PMMA thick sample 647 nm We have

  8. Laser Physics and Laser Spectroscopy.

    DTIC Science & Technology

    1986-03-01

    effect which limits the power throughout of a device; terbium qallium garnet (TGG), a Faraday isolator material; potassium niobate (KNbO 31 a nonlinear...extending the range of materials grown in fiber form. Two materials to be emphasized are terbium gallium garnet for optical isolators and potassium niobate...for doubling gallium arsenide diode lasers. References 1. R.H. Stolen, "Fiber Raman Lasers", Fiber and Integrated Optics, 3 (1980). 2. E. Ipoen and

  9. Laser therapy for cancer

    MedlinePlus

    ... this page: //medlineplus.gov/ency/patientinstructions/000905.htm Laser therapy for cancer To use the sharing features ... Lasers are also used on the skin. How Laser Therapy is Used Laser therapy can be used ...

  10. Laser beam monitoring system

    DOEpatents

    Weil, Bradley S.; Wetherington, Jr., Grady R.

    1985-01-01

    Laser beam monitoring systems include laser-transparent plates set at an angle to the laser beam passing therethrough and light sensor for detecting light reflected from an object on which the laser beam impinges.

  11. Laser Physics and Laser-Tissue Interaction

    PubMed Central

    Welch, A. J.; Torres, Jorge H.; Cheong, Wai-Fung

    1989-01-01

    Within the last few years, lasers have gained increasing use in the management of cardiovascular disease, and laser angioplasty has become a widely performed procedure. For this reason, a basic knowledge of lasers and their applications is essential to vascular surgeons, cardiologists, and interventional radiologists. To elucidate some fundamental concepts regarding laser physics, we describe how laser light is generated and review the properties that make lasers useful in medicine. We also discuss beam profile and spotsize, as well as dosimetric specifications for laser angioplasty. After considering laser-tissue interaction and light propagation in tissue, we explain how the aforementioned concepts apply to direct laser angioplasty and laser-balloon angioplasty. An understanding of these issues should prove useful not only in performing laser angioplasty but in comparing the reported results of various laser applications. (Texas Heart Institute Journal 1989;16:141-9) PMID:15227198

  12. Laser acceleration

    NASA Astrophysics Data System (ADS)

    Tajima, T.; Nakajima, K.; Mourou, G.

    2017-02-01

    The fundamental idea of Laser Wakefield Acceleration (LWFA) is reviewed. An ultrafast intense laser pulse drives coherent wakefield with a relativistic amplitude robustly supported by the plasma. While the large amplitude of wakefields involves collective resonant oscillations of the eigenmode of the entire plasma electrons, the wake phase velocity ˜ c and ultrafastness of the laser pulse introduce the wake stability and rigidity. A large number of worldwide experiments show a rapid progress of this concept realization toward both the high-energy accelerator prospect and broad applications. The strong interest in this has been spurring and stimulating novel laser technologies, including the Chirped Pulse Amplification, the Thin Film Compression, the Coherent Amplification Network, and the Relativistic Mirror Compression. These in turn have created a conglomerate of novel science and technology with LWFA to form a new genre of high field science with many parameters of merit in this field increasing exponentially lately. This science has triggered a number of worldwide research centers and initiatives. Associated physics of ion acceleration, X-ray generation, and astrophysical processes of ultrahigh energy cosmic rays are reviewed. Applications such as X-ray free electron laser, cancer therapy, and radioisotope production etc. are considered. A new avenue of LWFA using nanomaterials is also emerging.

  13. Laser construction

    SciTech Connect

    Martin, D.W.; Osterhage, R.J.; Summa, K.M.

    1989-02-14

    A laser device is described comprising an elongated laser medium of crystal material having a cylindrical shape modified to have a flat face formed on one side thereof, a highly heat conducting mounting member having a flat surface on a portion thereof, the medium being mounted on the mounting member with the flat face of the medium in face-to-face relation with the flat surface on the mounting member, a heat sink member having a surface for attaching the mounting member to, a pump source including an array of laser diodes each having opposite ends and positioned in side-by-side single file relation, a second highly heat conducting mounting member having a surface on which the array of laser diodes is positioned, the second mounting member being mounted on the heat sink member wherein the array of laser diodes are in substantial alignment with the axis of the medium along the side thereof opposite from the flat face of the medium.

  14. Tunable solid state lasers

    SciTech Connect

    Hammerling, R.; Budgor, A.B.; Pinto, A.

    1985-01-01

    This book presents the papers given at a conference on solid state lasers. Topics considered at the conference included transition-metal-doped lasers, line-narrowed alexandrite lasers, NASA specification, meteorological lidars, laser materials spectroscopy, laser pumped single pass gain, vibronic laser materials growth, crystal growth methods, vibronic laser theory, cross-fertilization through interdisciplinary fields, and laser action of color centers in diamonds.

  15. Laser cosmology

    NASA Astrophysics Data System (ADS)

    Chen, P.

    2014-05-01

    Recent years have witnessed tremendous progress in our understanding of the cosmos, which in turn points to even deeper questions to be further addressed. Concurrently the laser technology has undergone dramatic revolutions, providing exciting opportunity for science applications. History has shown that the symbiosis between direct observations and laboratory investigation is instrumental in the progress of astrophysics. We believe that this remains true in cosmology. Current frontier phenomena related to particle astrophysics and cosmology typically involve one or more of the following conditions: (1) extremely high energy events;(2) very high density, high temperature processes; (3) super strong field environments. Laboratory experiments using high intensity lasers can calibrate astrophysical observations, investigate underlying dynamics of astrophysical phenomena, and probe fundamental physics in extreme limits. In this article we give an overview of the exciting prospect of laser cosmology. In particular, we showcase its unique capability of investigating frontier cosmology issues such as cosmic accelerator and quantum gravity.

  16. Laser barometer

    DOEpatents

    Abercrombie, Kevin R.; Shiels, David; Rash, Tim

    2001-02-06

    A pressure measuring instrument that utilizes the change of the refractive index of a gas as a function of pressure and the coherent nature of a laser light to determine the barometric pressure within an environment. As the gas pressure in a closed environment varies, the index of refraction of the gas changes. The amount of change is a function of the gas pressure. By illuminating the gas with a laser light source, causing the wavelength of the light to change, pressure can be quantified by measuring the shift in fringes (alternating light and dark bands produced when coherent light is mixed) in an interferometer.

  17. Excimer lasers

    NASA Technical Reports Server (NTRS)

    Palmer, A. J.; Hess, L. D.; Stephens, R. R.

    1976-01-01

    A theoretical and experimental investigation into the possibility of achieving CW discharge pumped excimer laser oscillation is reported. Detailed theoretical modeling of capillary discharge pumping of the XeF and KXe and K2 excimer systems was carried out which predicted the required discharge parameters for reaching laser threshold on these systems. Capillary discharge pumping of the XeF excimer system was investigated experimentally. The experiments revealed a lower excimer level population density than predicted theoretically by about an order of magnitude. The experiments also revealed a fluorine consumption problem in the discharge in agreement with theory.

  18. Graviton laser

    NASA Astrophysics Data System (ADS)

    Landry, A.; Paranjape, M. B.

    2016-08-01

    We consider the possibility of creating a graviton laser. The lasing medium would be a system of contained, ultra cold neutrons. Ultra cold neutrons are a quantum mechanical system that interacts with gravitational fields and with the phonons of the container walls. It is possible to create a population inversion by pumping the system using the phonons. We compute the rate of spontaneous emission of gravitons and the rate of the subsequent stimulated emission of gravitons. The gain obtainable is directly proportional to the density of the lasing medium and the fraction of the population inversion. The applications of a graviton laser would be interesting.

  19. Laser Resonator

    NASA Technical Reports Server (NTRS)

    Harper, L. L. (Inventor)

    1983-01-01

    An optical resonator cavity configuration has a unitary mirror with oppositely directed convex and concave reflective surfaces disposed into one fold and concertedly reversing both ends of a beam propagating from a laser rod disposed between two total internal reflection prisms. The optical components are rigidly positioned with perpendicularly crossed virtual rooflines by a compact optical bed. The rooflines of the internal reflection prisms, are arranged perpendicularly to the axis of the laser beam and to the optical axes of the optical resonator components.

  20. Excimer lasers

    NASA Technical Reports Server (NTRS)

    Palmer, A. J.; Hess, L. D.; Stephens, R. R.; Pepper, D. M.

    1977-01-01

    The results of a two-year investigation into the possibility of developing continuous wave excimer lasers are reported. The program included the evaluation and selection of candidate molecular systems and discharge pumping techniques. The K Ar/K2 excimer dimer molecules and the xenon fluoride excimer molecule were selected for study; each used a transverse and capillary discharges pumping technique. Experimental and theoretical studies of each of the two discharge techniques applied to each of the two molecular systems are reported. Discharge stability and fluorine consumption were found to be the principle impediments to extending the XeF excimer laser into the continuous wave regime. Potassium vapor handling problems were the principal difficulty in achieving laser action on the K Ar/K2 system. Of the four molecular systems and pumping techniques explored, the capillary discharge pumped K Ar/K2 system appears to be the most likely candidate for demonstrating continuous wave excimer laser action primarily because of its predicted lower pumping threshold and a demonstrated discharge stability advantage.

  1. Laser Balancing

    NASA Astrophysics Data System (ADS)

    1981-01-01

    Mechanical Technology, Incorporated developed a fully automatic laser machining process that allows more precise balancing removes metal faster, eliminates excess metal removal and other operator induced inaccuracies, and provides significant reduction in balancing time. Manufacturing costs are reduced as a result.

  2. A New Clinical Instrument for The Early Detection of Cataract Using Dynamic Light Scattering and Corneal Topography

    NASA Technical Reports Server (NTRS)

    Ansari, Rafat R.; Datiles, Manuel B., III; King, James F.

    2000-01-01

    A growing cataract can be detected at the molecular level using the technique of dynamic light scattering (DLS). However, the success of this method in clinical use depends upon the precise control of the scattering volume inside a patient's eye and especially during patient's repeat visits. This is important because the scattering volume (cross-over region between the scattered fight and incident light) inside the eye in a high-quality DLS set-up is very small (few microns in dimension). This precise control holds the key for success in the longitudinal studies of cataract and during anti-cataract drug screening. We have circumvented these problems by fabricating a new DLS fiber optic probe with a working distance of 40 mm and by mounting it inside a cone of a corneal analyzer. This analyzer is frequently used in mapping the corneal topography during PRK (photorefractive keratectomy) and LASIK (laser in situ keratomileusis) procedures in shaping of the cornea to correct myopia. This new instrument and some preliminary clinical tests on one of us (RRA) showing the data reproducibility are described.

  3. A protocol for topographic-guided corneal repair utilizing the US Food and Drug Administration-approved Wavelight Contoura

    PubMed Central

    Motwani, Manoj

    2017-01-01

    Purpose To demonstrate how Wavelight Contoura can be used to repair corneas damaged by trauma and prior poor surgical outcomes. Methods Four representative eyes are presented that show different scenarios in which highly irregular corneas can be corrected with Wavelight Contoura using a protocol (named the San Diego Protocol) designed to use the information in Contoura processing. Both laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) were used. Results Highly aberrant corneas with large amounts of warpage can be corrected safely with the Wavelight Contoura system. The San Diego Protocol requires individual analysis of each case with decisions based on the level of warpage and the level of epithelial hyperplastic compensation. The need for a second refractive power equalization procedure should be planned for. Conclusion Contoura measured refraction can be integrally used as part of the San Diego Protocol to safely repair highly warped corneas. The refractive outcomes show dramatic improvement in vision, best-corrected visual acuity (BCVA), refraction, and topographic uniformity. PMID:28356712

  4. Transmittance and scattering during wound healing after refractive surgery

    NASA Astrophysics Data System (ADS)

    Mar, Santiago; Martinez-Garcia, C.; Blanco, J. T.; Torres, R. M.; Gonzalez, V. R.; Najera, S.; Rodriguez, G.; Merayo, J. M.

    2004-10-01

    Photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) are frequent techniques performed to correct ametropia. Both methods have been compared in their way of healing but there is not comparison about transmittance and light scattering during this process. Scattering in corneal wound healing is due to three parameters: cellular size and density, and the size of scar. Increase in the scattering angular width implies a decrease the contrast sensitivity. During wound healing keratocytes activation is induced and these cells become into fibroblasts and myofibroblasts. Hens were operated using PRK and LASIK techniques. Animals used in this experiment were euthanized, and immediately their corneas were removed and placed carefully into a cornea camera support. All optical measurements have been done with a scatterometer constructed in our laboratory. Scattering measurements are correlated with the transmittance -- the smaller transmittance is the bigger scattering is. The aim of this work is to provide experimental data of the corneal transparency and scattering, in order to supply data that they allow generate a more complete model of the corneal transparency.

  5. Laser Photochemistry.

    DTIC Science & Technology

    1981-07-01

    reaction due to decreased adsorption of the species on the catalytic surface. For example, i. . . 41 in the catalytic decomposition of formic acid ...over platinum (Ulmstead and Lin, 1978), the preexcitation of the gaseous formic acid molecules (by a 10 W/cm2 CW CO2 laser) resulted in a 50% increase...attention is given to selective and thermal excitation and the role of multiphonon couplings, heterogeneous catalysis , and chemical vapor deposition and

  6. Making a Laser Level

    ERIC Educational Resources Information Center

    Hawkins, Harry

    2004-01-01

    This article describes how to construct a laser level. This laser level can be made using a typical 4' (or shorter) bubble level and a small laser point. The laser unit is detachable, so the bubble level can also be used in the conventional way. However, the laser level works better than a simple bubble level. Making this inexpensive device is an…

  7. Infrared Lasers in Chemistry.

    ERIC Educational Resources Information Center

    John, Phillip

    1982-01-01

    Selected infrared laser chemistry topics are discussed including carbon dioxide lasers, infrared quanta and molecules, laser-induced chemistry, structural isomerization (laser purification, sensitized reactions, and dielectric breakdown), and fundamental principles of laser isotope separation, focusing on uranium isotope separation. (JN)

  8. Project LASER

    NASA Technical Reports Server (NTRS)

    1990-01-01

    NASA formally launched Project LASER (Learning About Science, Engineering and Research) in March 1990, a program designed to help teachers improve science and mathematics education and to provide 'hands on' experiences. It featured the first LASER Mobile Teacher Resource Center (MTRC), is designed to reach educators all over the nation. NASA hopes to operate several MTRCs with funds provided by private industry. The mobile unit is a 22-ton tractor-trailer stocked with NASA educational publications and outfitted with six work stations. Each work station, which can accommodate two teachers at a time, has a computer providing access to NASA Spacelink. Each also has video recorders and photocopy/photographic equipment for the teacher's use. MTRC is only one of the five major elements within LASER. The others are: a Space Technology Course, to promote integration of space science studies with traditional courses; the Volunteer Databank, in which NASA employees are encouraged to volunteer as tutors, instructors, etc; Mobile Discovery Laboratories that will carry simple laboratory equipment and computers to provide hands-on activities for students and demonstrations of classroom activities for teachers; and the Public Library Science Program which will present library based science and math programs.

  9. Laser nitriding and laser carburizing of surfaces

    NASA Astrophysics Data System (ADS)

    Schaaf, Peter

    2003-11-01

    Laser irradiation of surfaces with short pulses in reactive atmospheres (nitrogen, methane) can lead to very effective nitrification and carburization via complicated laser-surface-gas-plasma-interactions. This laser nitriding and laser carburizing and their basic underlying phenomena will be presented and partly explained by results of example materials (iron, titanium, aluminum, silicon) where nitride and carbide coatings can be formed by fast and easily by Excimer Laser, Nd:YAG laser, Free Electron Laser and also by femtosecond Ti:sapphire laser. This implies laser pulse durations from the nanosecond to the femtosecond regime and wavelengths from ultra-violet to infrared. The resulting surfaces, thin films, coatings and their properties are investigated by combining Mossbauer Spectroscopy, x-ray diffraction, x-ray absorption spectroscopy, Nanoindentation, Resonant Nuclear Reaction Analysis, and Rutherford Backscattering Spectroscopy.

  10. Laser therapy (image)

    MedlinePlus

    A laser is used for many medical purposes. Because the laser beam is so small and precise, it enables ... without injuring surrounding tissue. Some uses of the laser are retinal surgery, excision of lesions, and cauterization ...

  11. Lasers in Medicine.

    ERIC Educational Resources Information Center

    Hill, P. D.

    1989-01-01

    Described are the characteristics of the laser and its effects on the body. Discussed are examples of laser treatments, including angioplasty, ophthalmology, and dermatology. A discussion of lasers of clinical interest and their applications is presented. (YP)

  12. Laser-Driven Fusion.

    ERIC Educational Resources Information Center

    Gibson, A. F.

    1980-01-01

    Discusses the present status and future prospects of laser-driven fusion. Current research (which is classified under three main headings: laser-matter interaction processes, compression, and laser development) is also presented. (HM)

  13. Diode Laser Arrays

    NASA Astrophysics Data System (ADS)

    Botez, Dan; Scifres, Don R.

    2005-11-01

    Contributors; 1. Monolithic phase-locked semiconductor laser arrays D. Botez; 2. High power coherent, semiconductor laser master oscillator power amplifiers and amplifier arrays D. F. Welch and D. G. Mehuys; 3. Microoptical components applied to incoherent and coherent laser arrays J. R. Leger; 4. Modeling of diode laser arrays G. R. Hadley; 5. Dynamics of coherent semiconductor laser arrays H. G. Winfuland and R. K. Defreez; 6. High average power semiconductor laser arrays and laser array packaging with an emphasis for pumping solid state lasers R. Solarz; 7. High power diode laser arrays and their reliability D. R. Scifres and H. H. Kung; 8. Strained layer quantum well heterostructure laser arrays J. J. Coleman; 9. Vertical cavity surface emitting laser arrays C. J. Chang-Hasnain; 10. Individually addressed arrays of diode lasers D. Carlin.

  14. Lasers in Cancer Treatment

    MedlinePlus

    ... to treat cancer: carbon dioxide (CO 2 ) lasers, argon lasers, and neodymium: yttrium -aluminum-garnet (Nd:YAG) ... can be used with endoscopes. CO 2 and argon lasers can cut the skin’s surface without going ...

  15. Laser Weapons for Naval Applications

    DTIC Science & Technology

    2012-03-27

    IPG fiber lasers , 10 kW/ fiber 7 • Output wavelength is tunable (can operate in atmospheric window) Free Electron Lasers ...Multiple kilowatts over multiple kilometers • Laser power converters can be highly efficient, > 60 % • Fiber lasers are highly compact and... lasers - Free electron lasers • Background • Laser candidates • Additional capabilities - Power beaming 3 Laser Lethality -

  16. Laser accidents: Being Prepared

    SciTech Connect

    Barat, K

    2003-01-24

    The goal of the Laser Safety Officer and any laser safety program is to prevent a laser accident from occurring, in particular an injury to a person's eyes. Most laser safety courses talk about laser accidents, causes, and types of injury. The purpose of this presentation is to present a plan for safety offices and users to follow in case of accident or injury from laser radiation.

  17. Handbook of molecular lasers

    NASA Astrophysics Data System (ADS)

    Cheo, Peter K.

    The technology and applications of molecular lasers (MLs) are examined in chapters contributed by leading experts. Topics addressed include ML emission spectra, CO2 TEA lasers, RF-discharge-excited CO2 lasers, high-energy short-pulse CO2 lasers, high-power electron-beam-controlled CO2 lasers, HF/DF chemical lasers, optically pumped FIR MLs, and transients and instabilities in FIR MLs. Extensive diagrams, drawings, graphs, photographs, and tables of numerical data are provided.

  18. New laser protective eyewear

    NASA Astrophysics Data System (ADS)

    McLear, Mark

    1996-04-01

    Laser technology has significantly impacted our everyday life. Lasers are now used to correct your vision, clear your arteries, and are used in the manufacturing of such diverse products as automobiles, cigarettes, and computers. Lasers are no longer a research tool looking for an application. They are now an integral part of manufacturing. In the case of Class IV lasers, this explosion in laser applications has exposed thousands of individuals to potential safety hazards including eye damage. Specific protective eyewear designed to attenuate the energy of the laser beam below the maximum permissible exposure is required for Class 3B and Class IV lasers according to laser safety standards.

  19. Laser satellite power systems

    SciTech Connect

    Walbridge, E.W.

    1980-01-01

    A laser satellite power system (SPS) converts solar power captured by earth-orbiting satellites into electrical power on the earth's surface, the satellite-to-ground transmission of power being effected by laser beam. The laser SPS may be an alternative to the microwave SPS. Microwaves easily penetrate clouds while laser radiation does not. Although there is this major disadvantage to a laser SPS, that system has four important advantages over the microwave alternative: (1) land requirements are much less, (2) radiation levels are low outside the laser ground stations, (3) laser beam sidelobes are not expected to interfere with electromagnetic systems, and (4) the laser system lends itself to small-scale demonstration. After describing lasers and how they work, the report discusses the five lasers that are candidates for application in a laser SPS: electric discharge lasers, direct and indirect solar pumped lasers, free electron lasers, and closed-cycle chemical lasers. The Lockheed laser SPS is examined in some detail. To determine whether a laser SPS will be worthy of future deployment, its capabilities need to be better understood and its attractiveness relative to other electric power options better assessed. First priority should be given to potential program stoppers, e.g., beam attenuation by clouds. If investigation shows these potential program stoppers to be resolvable, further research should investigate lasers that are particularly promising for SPS application.

  20. [Laser physics].

    PubMed

    Banús Gassol, J M

    2008-11-01

    The commission of this article plunged me into doubt. First I should confess that I don't find excuse to escape this part if somebody wants to minimally deepen in the knowledge of the biological effects of this energy source. Secondly, when we talk about results, we use terms made and defined by Physics. Often we have polemics about results, and what really happens is that we don't reach agreements because we refer to different terms to explain the same observation; in conclusion we cannot understand each other because we do not know the adequate terms; for example, hypoxemia as oxygen deficit, which is true in an anemic patient as well as in a low oxygen saturation rate. In consequence, a good review of these concepts seems necessary to me. The third reason is the confusion that exists in our environment, I think sometimes of interest, about properties and effects of different types of laser. Only a minimal knowledge of physics will help us to state the scientific basis for understanding. The problems, nevertheless, accumulate due to the fact that the universe to which this article is directed is formed by urologists. What Physics education should we suppose they have? Superficial? Medium? Is it a collective with a uniform knowledge, being it whatever it is? The implication is clear. The article depth will depend on the answers to these questions. Nevertheless, the aim of the authors is to give a base enough to know what the laser is and how it acts. For that, the answer I gave to my questions is that the reader should understand the article and have enough base for, at least, reading critically the articles about laser published in urological journals.

  1. Measurements of striae in CR+ doped YAG laser crystals

    NASA Technical Reports Server (NTRS)

    Cady, Fredrick M.

    1994-01-01

    Striations in Czochralski (CZ) grown crystals have been observed in materials such as GaAs, silicon, photorefractive crystals used for data storage, potassium titanyl phosphate crystals and LiNbO3. Several techniques have been used for investigating these defects including electron microscopy, laser scanning tomography, selective photoetching, X-ray diffuse scattering, interference orthoscopy, laser interferometry and micro-Fourier transform infrared spectroscopy mapping. A 2mm thick sample of the material to be investigated is illuminated with light that is absorbed and non-absorbed by the ion concentration to be observed. The back surface of the sample is focused onto a solid-state image detector and images of the input beam and absorbed (and diffracted) beams are captured at two wavelengths. The variation of the coefficient of absorption asa function of distance on the sample can be derived from these measurements. A Big Sky Software Beamcode system is used to capture and display images. Software has been written to convert the Beamcode data files to a format that can be imported into a spreadsheet program such as Quatro Pro. The spreadsheet is then used to manipulate and display data. A model of the intensity map of the striae collected by the imaging system has been proposed and a data analysis procedure derived. From this, the variability of the attenuation coefficient alpha can be generated. Preliminary results show that alpha may vary by a factor of four or five over distances of 100 mu m. Potential errors and problems have been discovered and additional experiments and improvements to the experimental setup are in progress and we must now show that the measurement techniques and data analysis procedures provide 'real' information. Striae are clearly visible at all wavelengths including white light. Their basic spatial frequency does not change radically, at least when changing from blue to green to white light. Further experimental and theoretical work can

  2. The Geoscience Laser Altimeter System Laser Transmitter

    NASA Technical Reports Server (NTRS)

    Afzal, R. S.; Dallas, J. L.; Yu, A. W.; Mamakos, W. A.; Lukemire, A.; Schroeder, B.; Malak, A.

    2000-01-01

    The Geoscience Laser Altimeter System (GLAS), scheduled to launch in 2001, is a laser altimeter and lidar for tile Earth Observing System's (EOS) ICESat mission. The laser transmitter requirements, design and qualification test results for this space- based remote sensing instrument are presented.

  3. Studies on lasers and laser devices

    NASA Technical Reports Server (NTRS)

    Harris, S. E.; Siegman, A. E.; Young, J. F.

    1983-01-01

    The goal of this grant was to study lasers, laser devices, and uses of lasers for investigating physical phenomena are studied. The active projects included the development of a tunable, narrowband XUV light source and its application to the spectroscopy of core excited atomic states, and the development of a technique for picosecond time resolution spectroscopy of fast photophysical processes.

  4. Laser Spectroscopy

    NASA Astrophysics Data System (ADS)

    Katori, H.; Yoneda, H.; Nakagawa, K.; Shimizu, F.

    2010-02-01

    .] -- Ultracold Ytterbium atoms in optical lattices / S. Sugawa ... [et al.] -- Ultracold polar molecules in the rovibrational ground state / J. Deiglmayr ... [et al.] -- Polar molecules near quantum degeneracy / J. Ye and D. S. Jin -- Production of a quantum gas of rovibronic ground-state molecules in an optical lattice / J. G. Danzl ... [et al.] -- Recent progress in x-ray nonlinear optics / K. Tamasaku, K. Sawada, and T. Ishikawa -- Gas in scattering media absorption spectroscopy - laser spectroscopy in unconventional environments / S. Svanberg -- Laser spectroscopy on relativistic ion beams / S. Reinhardt ... [et al.] -- Single frequency microcavity lasers and applications / L. Xu ... [et al.].

  5. Reverse laser drilling

    NASA Technical Reports Server (NTRS)

    Anthony, Thomas R. (Inventor)

    1984-01-01

    This invention provides a method for laser drilling small diameter, closely-spaced, and accurately located holes in a body of material which is transparent or substantially transparent to the laser radiation employed whereby the holes are drilled through the thickness of the body from the surface opposite to that on which the laser beam impinges to the surface of laser beam impingement.

  6. Laser photobiology and photomedicine

    SciTech Connect

    Martellucci, S.; Chester, A.N.

    1985-01-01

    This book presents information on the following topics: the physical and biological basis of photobiology and photomedicine; the biological effects and applications of laser technology; photochemotherapy; photobiology and dermatology; surgical and ophthalmological applications of lasers; laser safety; and diagnostics and technological aspects of recent laser developments.

  7. Narrow gap laser welding

    DOEpatents

    Milewski, J.O.; Sklar, E.

    1998-06-02

    A laser welding process including: (a) using optical ray tracing to make a model of a laser beam and the geometry of a joint to be welded; (b) adjusting variables in the model to choose variables for use in making a laser weld; and (c) laser welding the joint to be welded using the chosen variables. 34 figs.

  8. Narrow gap laser welding

    DOEpatents

    Milewski, John O.; Sklar, Edward

    1998-01-01

    A laser welding process including: (a) using optical ray tracing to make a model of a laser beam and the geometry of a joint to be welded; (b) adjusting variables in the model to choose variables for use in making a laser weld; and (c) laser welding the joint to be welded using the chosen variables.

  9. Obstacles to Laser Safety

    SciTech Connect

    Barat, K

    2005-04-25

    The growth of laser development & technology has been remarkable. Unfortunately, a number of traps or obstacles to laser safety have also developed with that growth. The goal of this article is to highlight those traps, in the hope that an aware laser user will avoid them. These traps have been the cause or contributing factor of many a preventable laser accident.

  10. Short wavelength laser

    DOEpatents

    Hagelstein, P.L.

    1984-06-25

    A short wavelength laser is provided that is driven by conventional-laser pulses. A multiplicity of panels, mounted on substrates, are supported in two separated and alternately staggered facing and parallel arrays disposed along an approximately linear path. When the panels are illuminated by the conventional-laser pulses, single pass EUV or soft x-ray laser pulses are produced.

  11. Longitudinal discharge laser baffles

    DOEpatents

    Warner, B.E.; Ault, E.R.

    1994-06-07

    The IR baffles placed between the window and the electrode of a longitudinal discharge laser improve laser performance by intercepting off-axis IR radiation from the laser and in doing so reduce window heating and subsequent optical distortion of the laser beam. 1 fig.

  12. Longitudinal discharge laser baffles

    DOEpatents

    Warner, Bruce E.; Ault, Earl R.

    1994-01-01

    The IR baffles placed between the window and the electrode of a longitudinal discharge laser improve laser performance by intercepting off-axis IR radiation from the laser and in doing so reduce window heating and subsequent optical distortion of the laser beam.

  13. Solar driven lasers for power satellite applications

    NASA Technical Reports Server (NTRS)

    Taussio, R.; Cassady, P.; Klosterman, E.

    1980-01-01

    The technological feasibility of using multimagawatt lasers for space power transmission is discussed. Candidate lasers include electric discharge lasers, direct optically pumped lasers, and free electron lasers.

  14. What is a Laser?

    NASA Astrophysics Data System (ADS)

    Julien, Lucile; Schwob, Catherine

    2015-10-01

    The first laser was built more than 50 years ago, inMay 1960: it was a pulsed ruby laser. It was a simple laboratory curiosity and nobody knew what its usefulness could be. Other devices were rapidly demonstrated, and the variety and number of lasers in the world increased at a huge rate. Currently, the annual laser world market is worth about 6 billion dollars. Thanks to the remarkable properties of laser light, laser applications increase steadily in the domains of industry, building, medicine, telecommunications, etc. One can find many lasers in research laboratories, and they are used more and more in our everyday life and almost everybody has already seen a laser beam. The goal of the first chapter of this book is to explain simply what a laser is, how it is built and how it operates. Firstly, let us point out the outstanding properties of the laser light.

  15. Tunable lasers- an overview

    SciTech Connect

    Guenther, B.D.; Buser, R.G.

    1982-08-01

    This overview of tunable lasers describes their applicability to spectroscopy in the ultraviolet and middle infrared ranges; to rapid on-line diagnostics by ultrashort cavity lasers; to exploration, by the free electron laser, for its wide tuning in the far infrared to submillimeter region; to remote detection, in areas such as portable pollution monitors, on-line chemical analyzers, auto exhaust analyzers, and production line controls; to photochemistry; and to other potential areas in diagnostics, communications, and medical and biological sciences. The following lasers are characterized by their tunability: solid state lasers, primarily alexandrite, with a tuning range of ca 1000 Angstroms; color center lasers; semiconductor lasers; dye lasers; gas lasers, where high-pressure CO/sub 2/ discharges are the best known example for a wide tunability range, and research is continuing in systems such as the alkali dimers; and, at wavelengths beyond 10 micrometers, the possibilities beyond Cerenkov and free electron lasers.

  16. Lasers in flow cytometry.

    PubMed

    Telford, William G

    2011-01-01

    Laser technology has advanced tremendously since the first gas lasers were incorporated into early flow cytometers. Gas lasers have been largely replaced by solid-state laser technology, making virtually any desirable visible light wavelength available for flow cytometry. Multiwavelength, white light, and wavelength tunable lasers are poised to enhance our analytical capabilities even further. In this chapter, I summarize the role that lasers play in cytometry, and the practical characteristics that make a laser appropriate for flow cytometry. I then review the latest single wavelength lasers available for flow cytometry, and how they can be used to excite the ever-expanding array of available fluorochromes. Finally, I review the contribution and potential of the latest tunable laser technology to flow cytometry, and show several examples of these novel sources integrated into production instruments. Technical details and critical parameters for successful application of these lasers for biomedical analysis are covered in depth.

  17. Surgical lasers in dermatology

    NASA Astrophysics Data System (ADS)

    Szymanczyk, Jacek; Nowakowski, Wlodzimierz; Golebiowska, Aleksandra; Michalska, I.; Mindak, Marek K.

    1997-10-01

    Almost every laser for medical applications was first tried in dermatology. The efficiency of YAG, CO2, and Argon lasers on this area and their potential advantages over conventional methods were mostly evaluated by cosmetic effect of laser therapy. The indications for different laser treatment in such dermatological cases as: angiomas, telangiectasias, pigmented lesions, nevus flammeus congenitus, deep cavernous angiomas, skin neoplasms and condylomata acuminata are discussed in this paper and the results of the laser therapy are also presented.

  18. Laser Reliability Prediction

    DTIC Science & Technology

    1975-08-01

    Lasers, Quality Level 1 - Group 2 32 5.3-3 Kolmogorov-Smirnoff Test - Helium/Neon Lasers, Quality Level 1 33 5.3-4 Welbull Analysis...institutions through- out the United States and Canada. The collected laser data were grouped, analyzed, and statistically tested for homogeneity...sources were Initially contacted by letter questionnaires In which personnel were requested to describe any laser component life test or laser system

  19. Intracavity Raman lasers

    SciTech Connect

    Band, Y.B.; Ackerhalt, J.R.; Krasinski, J.S.; Heller, D.F.

    1989-02-01

    Experimental and theoretical studies of intracavity Raman lasers are presented. Advantages of intracavity Raman lasers, particularly for low-emission cross section and broadly tunable vibronic gain media, are described. Experimental studies of a hydrogen gas Raman laser pumped inside the cavity of an alexandrite laser are presented. A theoretical model of the dynamics of a unidirectional intracavity Raman ring laser is developed and solved analytically. This model is adapted to simulate experiments.

  20. Mercury Bromide Laser Research.

    DTIC Science & Technology

    1981-05-04

    Discharge", Optics Lett., 2(3), (March 1978). 7. R. Burnham, "Discharge Pumped Mercuric Halide Dissociation Lasers", Appl. Phys. Lett., 33: 15 (July 1978...laser and fluorescence signals. Neutral density filters served to prevent saturation of the detector during the laser measurements. F. Laser Output as a...REFERENCES . E. J. Schimitschek and J. E. Celto, " Mercuric Bromide Dissociation Laser in an Electric Discharge," Optics Lett. 2(3), March 1978. This

  1. The history of LASIK.

    PubMed

    Reinstein, Dan Z; Archer, Timothy J; Gobbe, Marine

    2012-04-01

    Keratomileusis, brainchild of Jose I. Barraquer Moner, was conceived and developed as the first stromal sculpting method to correct refractive error in 1948. The word "keratomileusis" literally means "sculpting" of the "cornea." Barraquer's first procedures involved freezing a disc of anterior corneal tissue before removing stromal tissue with a lathe. Over the years, the procedure continued to develop, first through the Barraquer-Krumeich-Swinger non-freeze technique where tissue was removed from the underside of the disc by a second pass of the microkeratome. In-situ keratomileusis was later developed by passing the microkeratome a second time directly on the stromal bed. The procedure became known as automated lamellar keratoplasty with the invention of an automated microkeratome and was further refined by replacing the disc without sutures and later by stopping the microkeratome before the end of the pass to create a hinged flap, as first demonstrated in 1989. The history of the excimer laser dates back to 1900 and the quantum theory, eventually leading to the discovery that 193-nm ultraviolet excimer laser pulses could photoablate tissue without thermal damage. Ultrastructural and wound healing studies confirmed that large area ablation could be performed in the central cornea. This was described as photorefractive keratectomy in 1986 and the first sighted eyes were treated in 1988. An excimer laser was first used to sculpt from the stromal bed under a hinged flap created manually using a trephine and scalpel in 1988. The incorporation of a microkeratome in 1990 finally led to laser in situ keratomileusis-LASIK-as we know it today.

  2. Nanocrystal waveguide (NOW) laser

    DOEpatents

    Simpson, John T.; Simpson, Marcus L.; Withrow, Stephen P.; White, Clark W.; Jaiswal, Supriya L.

    2005-02-08

    A solid state laser includes an optical waveguide and a laser cavity including at least one subwavelength mirror disposed in or on the optical waveguide. A plurality of photoluminescent nanocrystals are disposed in the laser cavity. The reflective subwavelength mirror can be a pair of subwavelength resonant gratings (SWG), a pair of photonic crystal structures (PC), or a distributed feedback structure. In the case of a pair of mirrors, a PC which is substantially transmissive at an operating wavelength of the laser can be disposed in the laser cavity between the subwavelength mirrors to improve the mode structure, coherence and overall efficiency of the laser. A method for forming a solid state laser includes the steps of providing an optical waveguide, creating a laser cavity in the optical waveguide by disposing at least one subwavelength mirror on or in the waveguide, and positioning a plurality of photoluminescent nanocrystals in the laser cavity.

  3. Infrared laser system

    DOEpatents

    Cantrell, Cyrus D.; Carbone, Robert J.; Cooper, Ralph

    1982-01-01

    An infrared laser system and method for isotope separation may comprise a molecular gas laser oscillator to produce a laser beam at a first wavelength, Raman spin flip means for shifting the laser to a second wavelength, a molecular gas laser amplifier to amplify said second wavelength laser beam to high power, and optical means for directing the second wavelength, high power laser beam against a desired isotope for selective excitation thereof in a mixture with other isotopes. The optical means may include a medium which shifts the second wavelength high power laser beam to a third wavelength, high power laser beam at a wavelength coincidental with a corresponding vibrational state of said isotope and which is different from vibrational states of other isotopes in the gas mixture.

  4. Infrared laser system

    DOEpatents

    Cantrell, Cyrus D.; Carbone, Robert J.; Cooper, Ralph S.

    1977-01-01

    An infrared laser system and method for isotope separation may comprise a molecular gas laser oscillator to produce a laser beam at a first wavelength, Raman spin flip means for shifting the laser to a second wavelength, a molecular gas laser amplifier to amplify said second wavelength laser beam to high power, and optical means for directing the second wavelength, high power laser beam against a desired isotope for selective excitation thereof in a mixture with other isotopes. The optical means may include a medium which shifts the second wavelength high power laser beam to a third wavelength, high power laser beam at a wavelength coincidental with a corresponding vibrational state of said isotope and which is different from vibrational states of other isotopes in the gas mixture.

  5. Laser Surveying

    NASA Technical Reports Server (NTRS)

    1978-01-01

    NASA technology has produced a laser-aided system for surveying land boundaries in difficult terrain. It does the job more accurately than conventional methods, takes only one-third the time normally required, and is considerably less expensive. In surveying to mark property boundaries, the objective is to establish an accurate heading between two "corner" points. This is conventionally accomplished by erecting a "range pole" at one point and sighting it from the other point through an instrument called a theodolite. But how do you take a heading between two points which are not visible to each other, for instance, when tall trees, hills or other obstacles obstruct the line of sight? That was the problem confronting the U.S. Department of Agriculture's Forest Service. The Forest Service manages 187 million acres of land in 44 states and Puerto Rico. Unfortunately, National Forest System lands are not contiguous but intermingled in complex patterns with privately-owned land. In recent years much of the private land has been undergoing development for purposes ranging from timber harvesting to vacation resorts. There is a need for precise boundary definition so that both private owners and the Forest Service can manage their properties with confidence that they are not trespassing on the other's land.

  6. Complex investigations of structural and optical homogeneities of low-photorefractivity lithium niobate crystals by the conoscopy and photoinduced and Raman light scattering methods

    NASA Astrophysics Data System (ADS)

    Sidorov, N. V.; Pikoul, O. Yu.; Kruk, A. A.; Teplyakova, N. A.; Yanichev, A. A.; Palatnikov, M. N.

    2015-02-01

    Using photoinduced light scattering, conoscopy, and Raman spectroscopy methods, we have studied stoichiometric lithium niobate crystals and congruent crystals that were doped with Mg(0.078, 0.89 mas %), Zn(0.03, 0.52, 0.62), Cu(0.015), B(0.12), Gd(0.51), Y(0.46), Gd(0.23):Mg(0.75), Mg(0.86):Fe(0.0036), Ta(1.13):Mg(0.011), and Y(0.24):Mg(0.63) cations. It has been found that, depending on the kind of the pattern of photoinduced light scattering, investigated specimens can be divided into three groups. We have shown that the asymmetry of the indicatrix of photoinduced light scattering of LiNbO3 crystals is caused by birefringence of exciting laser radiation as it propagates perpendicularly to the polar axis of the crystal, whereas the asymmetry of the Raman spectrum arises due to the occurrence of spontaneous polarization, the vector of which is directed along the polar axis, and by birefringence. The pattern of the photoinduced light scattering depends on the difference of the refractive indices Δ n = n o - n e of the ordinary ( n o ) and extraordinary ( n e ) rays and their energies E. If En o {ie259-1} En e , the proportion of the photoinduced light scattering has the shape of a three-layer round spot. For equal energies, the pattern has the shape of a symmetric figure-eight. At En o < En e , the figure-eight is asymmetric. In this case, its large "lobe" is directed in the positive direction of the polar axis of the crystal.

  7. Alexandrite laser pumped by semiconductor lasers

    SciTech Connect

    Scheps, R.; Gately, B.M.; Myers, J.F. ); Krasinski, J.S. ); Heller, D.F. )

    1990-06-04

    We report the first operation of a direct diode-pumped tunable chromium-doped solid-state laser. A small alexandrite (Cr:BeAl{sub 2}O{sub 4}) crystal was longitudinally pumped by two visible laser diodes. The threshold pump power was 12 mW using the {ital R}{sub 1} line at 680.4 nm for the pump transition, and the slope efficiency was 25%. The measured laser output bandwidth was 2.1 nm.

  8. Alexandrite laser pumped by semiconductor lasers

    NASA Astrophysics Data System (ADS)

    Scheps, Richard; Gately, Bernard M.; Myers, Joseph F.; Krasinski, Jerzy S.; Heller, Donald F.

    1990-06-01

    We report the first operation of a direct diode-pumped tunable chromium-doped solid-state laser. A small alexandrite (Cr:BeAl2O4) crystal was longitudinally pumped by two visible laser diodes. The threshold pump power was 12 mW using the R1 line at 680.4 nm for the pump transition, and the slope efficiency was 25%. The measured laser output bandwidth was 2.1 nm.

  9. Lasers in aviation

    NASA Astrophysics Data System (ADS)

    Goncharov, I. N.; Dezhin, V. N.; Kutakhov, V. P.; Petukhov, A. V.; Sidorin, V. M.; Sukhar, I. M.

    The way in which lasers are being incorporated into the military aircraft of the United States and the countries of Western Europe is discussed. Descriptions are given of laser weapons-guiding systems (including ranger finders and systems for target illumination), laser systems for navigation and flight-safety assurance (gyroscopes, velocity gauges, altimeters, systems providing meteorological data, proximity warning systems), and laser systems for air reconnaissance, communications, and control. Attention is also given to the Glissada laser guide path system, developed in the USSR. The physics of the systems is emphasized in the description and the principles underlying the operation of a laser are discussed in the introduction.

  10. Lasers in periodontics.

    PubMed

    Elavarasu, Sugumari; Naveen, Devisree; Thangavelu, Arthiie

    2012-08-01

    Laser is one of the most captivating technologies in dental practice since Theodore Maiman in 1960 invented the ruby laser. Lasers in dentistry have revolutionized several areas of treatment in the last three and a half decades of the 20(th) century. Introduced as an alternative to mechanical cutting device, laser has now become an instrument of choice in many dental applications. Evidence suggests its use in initial periodontal therapy, surgery, and more recently, its utility in salvaging implant opens up a wide range of applications. More research with better designs are a necessity before lasers can become a part of dental armamentarium. This paper gives an insight to laser in periodontics.

  11. Tunable chromium lasers

    SciTech Connect

    Chase, L.L.; Payne, S.A.

    1989-01-01

    During the decade that has passed since the discovery of the alexandrite laser, many other tunable vibronic sideband lasers based on Cr/sup 3 +/ have been developed. These lasers span the wavelength range from 700 nm to at least 1235 nm. Experimental and theoretical research has provided an understanding of the important factors that influence the performance of these Cr/sup 3 +/ lasers and other solid state vibronic lasers. The intrinsic performance levels of some of the most promising Cr/sup 3 +/ lasers are evaluated from extrapolated slope efficiency measurements. 7 refs., 4 figs., 2 tabs.

  12. Maser and laser engineering

    SciTech Connect

    Ishii, T.K.

    1980-01-01

    This book is intended to be a textbook for an upper division one-semester electrical engineering course. Students are expected to have had some undegraduate course work in modern physics and in electromagnetic field theory. General aspects regarding devices based on quantum electronics are considered along with gas masers, solid masers, gas lasers, solid lasers, semiconductor lasers, liquid lasers, modulation techniques for lasers, and opto-electrical demodulators and energy convertors. Attention is given to quantum electric harmonic generators, Raman lasers, optical parametric interactions, holograms, optical terms, crystallographic terms, band theory, Schroedinger formulation and Dirac formation, and the quantum number of electrons in a hydrogen atom.

  13. Laser peening of metals- enabling laser technology

    SciTech Connect

    Dane, C.B.; Hackel, L.A.; Daly, J.; Harrisson, J.

    1997-11-13

    Laser peening, a surface treatment for metals, employs laser induced shocks to create deep and intense residual stresses in critical components. In many applications this technology is proving to be superior to conventional treatments such as shot peening. The laser peening process has generated sufficiently impressive results to move it from a laboratory demonstration phase into a significant industrial process. However until now this evolution has been slowed because a laser system meeting the average power requirements for a high throughput process has been lacking.

  14. Laser Spectroscopy

    NASA Astrophysics Data System (ADS)

    Hollberg, Leo; Bergquist, James Charles; Kasevich, Mark A.

    2008-04-01

    Degenerate gases. Probing vortex pair sizes in the Berezinskii-Kosterlitz-Thouless regime on a two-dimensional lattice of Bose-Einstein condensates / V. Schweikhard ... [et al.]. Interacting Bose-Einstein condensates in random potentials / P. Bouyer ... [et al.]. Towards quantum magnetism with ultracold atoms in optical lattices / I. Bloch -- Precision measurement and fundamental physics. T-violation and the search for a permanent electric dipole moment of the mercury atom / E. N. Fortson -- Quantum information and control I. Quantum information processing and ramsey spectroscopy with trapped ions / C. F. Roos ... [et al.]. Quantum non-demolition counting of photons in a cavity / S. Haroche ... [et al.] -- Ultra-fast control and spectroscopy. Frequency-Comb- assisted mid-infrared spectroscopy / P. de Natale ... [et al.] -- Precision measurement and applications. Precision gravity tests by atom interferometry / G. M. Tino ... [et al.] -- Novel spectroscopic applications. On a variation of the proton-electron mass ratio / W. Ubachs ... [et al.] -- Quantum information and control II. Quantum interface between light and atomic ensembles / H. Krauter ... [et al.] -- Degenerate Fermi gases. An atomic Fermi gas near a P-wave Feshbach resonance / D. S. Jin, J. P. Gaebler and J. T. Stewart. Bragg scattering of correlated atoms from a degenerate Fermi gas / R. J. Ballagh, K. J. Challis and C. W. Gardiner -- Spectroscopy and control of atoms and molecules. Stark and Zeeman deceleration of neutral atoms and molecules / S. D. Hogan ... [et al.]. Generation of coherent, broadband and tunable soft x-ray continuum at the leading edge of the driver laser pulse / A. Jullien ... [et al.]. Controlling neural atoms and photons with optical conveyor belts and ultrathin optical fibers / D. Meschede. W. Alt and A. Rauschenbeutel -- Spectroscopy on the small scale. Wide-field cars-microscopy / C. Heinrich ... [et al.]. Atom nano-optics and nano-lithography / V. I. Balykin ... [et al

  15. Laser amplifier and method

    DOEpatents

    Backus, Sterling; Kapteyn, Henry C.; Murnane, Margaret M.

    1997-01-01

    Laser amplifiers and methods for amplifying a laser beam are disclosed. A representative embodiment of the amplifier comprises first and second curved mirrors, a gain medium, a third mirror, and a mask. The gain medium is situated between the first and second curved mirrors at the focal point of each curved mirror. The first curved mirror directs and focuses a laser beam to pass through the gain medium to the second curved mirror which reflects and recollimates the laser beam. The gain medium amplifies and shapes the laser beam as the laser beam passes therethough. The third mirror reflects the laser beam, reflected from the second curved mirror, so that the laser beam bypasses the gain medium and return to the first curved mirror, thereby completing a cycle of a ring traversed by the laser beam. The mask defines at least one beam-clipping aperture through which the laser beam passes during a cycle. The gain medium is pumped, preferably using a suitable pumping laser. The laser amplifier can be used to increase the energy of continuous-wave or, especially, pulsed laser beams including pulses of femtosecond duration and relatively high pulse rate.

  16. Laser amplifier and method

    DOEpatents

    Backus, S.; Kapteyn, H.C.; Murnane, M.M.

    1997-07-01

    Laser amplifiers and methods for amplifying a laser beam are disclosed. A representative embodiment of the amplifier comprises first and second curved mirrors, a gain medium, a third mirror, and a mask. The gain medium is situated between the first and second curved mirrors at the focal point of each curved mirror. The first curved mirror directs and focuses a laser beam to pass through the gain medium to the second curved mirror which reflects and recollimates the laser beam. The gain medium amplifies and shapes the laser beam as the laser beam passes therethrough. The third mirror reflects the laser beam, reflected from the second curved mirror, so that the laser beam bypasses the gain medium and return to the first curved mirror, thereby completing a cycle of a ring traversed by the laser beam. The mask defines at least one beam-clipping aperture through which the laser beam passes during a cycle. The gain medium is pumped, preferably using a suitable pumping laser. The laser amplifier can be used to increase the energy of continuous-wave or, especially, pulsed laser beams including pulses of femtosecond duration and relatively high pulse rate. 7 figs.

  17. Phased laser array for generating a powerful laser beam

    DOEpatents

    Holzrichter, John F.; Ruggiero, Anthony J.

    2004-02-17

    A first injection laser signal and a first part of a reference laser beam are injected into a first laser element. At least one additional injection laser signal and at least one additional part of a reference laser beam are injected into at least one additional laser element. The first part of a reference laser beam and the at least one additional part of a reference laser beam are amplified and phase conjugated producing a first amplified output laser beam emanating from the first laser element and an additional amplified output laser beam emanating from the at least one additional laser element. The first amplified output laser beam and the additional amplified output laser beam are combined into a powerful laser beam.

  18. Simultaneous topography-guided PRK followed by corneal collagen cross-linking after lamellar keratoplasty for keratoconus

    PubMed Central

    Spadea, Leopoldo; Paroli, Marino

    2012-01-01

    Background The purpose of this paper is to report the results of using combined treatment of customized excimer laser-assisted photorefractive keratectomy (PRK) and prophylactic corneal collagen crosslinking (CXL) for residual refractive error in a group of patients who had previously undergone lamellar keratoplasty for keratoconus. Methods The study included 14 eyes from 14 patients who had originally been treated for keratoconus in one eye by excimer laser-assisted lamellar keratoplasty (ELLK), and subsequently presented with residual ametropia (−6.11 D ± 2.48, range −2.50 to −9.50). After a mean 40.1 ± 12.4 months since ELLK they underwent combined simultaneous corneal regularization treatment with topographically guided transepithelial excimer laser PRK (central corneal regularization) and corneal CXL induced by riboflavin-ultraviolet A. Results After a mean 15 ± 6.5 (range 6–24) months, all eyes gained at least one Snellen line of uncorrected distance visual acuity (range 1–10). No patient lost lines of corrected distance visual acuity, and four patients gained three lines of corrected distance visual acuity. Mean manifest refractive spherical equivalent was −0.79 ± 2.09 (range +1 to −3.0) D, and topographic keratometric astigmatism was 5.02 ± 2.93 (range 0.8–8.9) D. All the corneas remained clear (haze < 1). Conclusion The combination of customized PRK and corneal CXL provided safe and effective results in the management of corneal regularization for refractive purposes after ELLK for keratoconus. PMID:23152658

  19. Laser particle sorter

    DOEpatents

    Martin, J.C.; Buican, T.N.

    1987-11-30

    Method and apparatus are provided for sorting particles, such as biological particles. A first laser is used to define an optical path having an intensity gradient which is effective to propel the particles along the path but which is sufficiently weak that the particles are not trapped in an axial direction. A probe laser beam is provided for interrogating the particles to identify predetermined phenotypical characteristics of the particles. A second laser beam is provided to intersect the driving first laser beam, wherein the second laser beam is activated by an output signal indicative of a predetermined characteristic. The second laser beam is switchable between a first intensity and a second intensity, where the first intensity is effective to displace selected particles from the driving laser beam and the second intensity is effective to propel selected particles along the deflection laser beam. The selected particles may then be propelled by the deflection beam to a location effective for further analysis. 2 figs.

  20. Laser particle sorter

    DOEpatents

    Martin, John C.; Buican, Tudor N.

    1989-01-01

    Method and apparatus for sorting particles, such as biological particles. A first laser defines an optical path having an intensity gradient which is effective to propel the particles along the path but which is sufficiently weak that the particles are not trapped in an axial direction. A probe laser beam interrogates the particles to identify predetermined phenotypical characteristics of the particles. A second laser beam intersects the driving first laser beam, wherein the second laser beam is activated by an output signal indicative of a predetermined characteristic. The second laser beam is switchable between a first intensity and a second intensity, where the first intensity is effective to displace selected particles from the driving laser beam and the second intensity is effective to propel selected particles along the deflection laser beam. The selected particles may then be propelled by the deflection beam to a location effective for further analysis.

  1. Slender tip laser scalpel

    DOEpatents

    Veligdan, James T.

    2004-01-06

    A laser scalpel includes a ribbon optical waveguide extending therethrough and terminating at a slender optical cutting tip. A laser beam is emitted along the height of the cutting tip for cutting tissue therealong.

  2. Laser device and method

    SciTech Connect

    Myers, J. D.

    1985-06-25

    A simplified, relatively inexpensive laser device, wherein the laser elements are fixed in a body exoskeleton of electrical insulating material having a low coefficient of thermal expansion. The preferred embodiment includes a shotgun type laser filter having parallel bores which receive the laser flashlamp and laser rod in fixed relation in a body chamber. The reflector surrounds the laser filter and retains the filter within the body chamber. In the preferred method of this invention, several controlled lasing pulses are generated with each illumination pulse of the flashlamp, substantially increasing the efficiency of the laser device. The number of pulses is generally controlled by increasing the voltage to the flashlamp. The rapid multiple lasing pulses generate an elongated plasma in a fluid medium, such as the vitreous fluid body of an eye which makes the laser device extemely efficient for treating glaucoma and other medical treatments.

  3. Laser hair removal.

    PubMed

    Wanner, Molly

    2005-01-01

    Since 1996, there have been numerous advances in hair laser removal that utilize melanin as a chromophore. All of the devices on the market may be used in patients with light skin (phototypes I-III) and yield hair reduction near 75%. The ruby (694 nm) laser, alexandrite (755 nm) laser, and diode (810 nm) laser, as well as intense pulsed light are commonly used devices for hair laser removal. The long-pulsed Nd:YAG (1064 nm) laser represents the safest device for hair removal in dark-skinned patients because of its long wavelength, although the diode laser, alexandrite laser, and intense pulse light may be used. For treatment of light hair, combination radiofrequency and optical devices as well as photodynamic therapy are under investigation.

  4. Laser Radar Animation

    NASA Video Gallery

    Laser and radar instruments aboard NASA aircraft provide measurements of the snow and ice surface and down to the bedrock under the ice. Lasers, with a shorter wavelength, measure the surface eleva...

  5. Direct nuclear pumped laser

    DOEpatents

    Miley, George H.; Wells, William E.; DeYoung, Russell J.

    1978-01-01

    There is provided a direct nuclear pumped gas laser in which the lasing mechanism is collisional radiated recombination of ions. The gas laser active medium is a mixture of the gases, with one example being neon and nitrogen.

  6. Laser surgery - skin

    MedlinePlus

    Surgery using a laser ... used is directly related to the type of surgery being performed and the color of the tissue ... Laser surgery can be used to: Close small blood vessels to reduce blood loss Remove warts , moles , sunspots, and ...

  7. Laser programs highlights 1993

    SciTech Connect

    1995-06-01

    Over the last two decades, the scope of our laser research has grown immensely. The small, low-power laser systems of our early days have given way to laser systems of record-breaking size and power. Now we are focusing our activities within the target physics and laser science programs to support the ignition and gain goals of the proposed glass-laser National Ignition Facility. In our laser isotope separation work, we completed the most important set of experiments in the history of the AVLIS Program in 1993, which culminated in a spectacularly successful run that met or exceeded all our objectives. We are also developing lasers and laser-related technologies for a variety of energy, commercial, and defense uses. On the horizon are transfers of important technologies for waste treatment, x-ray lithography, communications and security, optical imaging, and remote sensing, among others.

  8. MESSENGER Laser Altimeter

    NASA Video Gallery

    MESSENGER's Mercury Laser Altimeter sends out laser pulses that hit the ground and return to the instrument. The amount of light that returns for each pulse gives the reflectance at that point on t...

  9. Carbon dioxide slab laser

    SciTech Connect

    Tulip, J.

    1988-01-12

    A gas slab laser is described comprising: first and second elongated electrodes each including a planar light reflecting surface disposed so as to form a light guide only in a plane perpendicular to the planar surface and to define a gas discharge gap therebetween; a laser gas disposed in the gap; and means for applying a radio frequency current between the first and second electrodes to establish a laser-exciting discharge in the laser gas.

  10. CO2 laser modeling

    NASA Technical Reports Server (NTRS)

    Johnson, Barry

    1992-01-01

    The topics covered include the following: (1) CO2 laser kinetics modeling; (2) gas lifetimes in pulsed CO2 lasers; (3) frequency chirp and laser pulse spectral analysis; (4) LAWS A' Design Study; and (5) discharge circuit components for LAWS. The appendices include LAWS Memos, computer modeling of pulsed CO2 lasers for lidar applications, discharge circuit considerations for pulsed CO2 lidars, and presentation made at the Code RC Review.

  11. Alkali-vapor lasers

    NASA Astrophysics Data System (ADS)

    Zweiback, J.; Komashko, A.; Krupke, W. F.

    2010-02-01

    We report on the results from several of our alkali laser systems. We show highly efficient performance from an alexandrite-pumped rubidium laser. Using a laser diode stack as a pump source, we demonstrate up to 145 W of average power from a CW system. We present a design for a transversely pumped demonstration system that will show all of the required laser physics for a high power system.

  12. Laser shaping of cartilage

    NASA Astrophysics Data System (ADS)

    Sobol, Emil N.; Bagratashvili, Victor N.; Omelchenko, Alexander I.; Sviridov, Alexander P.; Helidonis, Emmanuel S.; Kavvalos, George; Christodoulou, P. N.; Naoumidi, I.; Velegrakis, G.; Ovchinnikov, Yuriy M.; Shechter, A.

    1994-09-01

    The carbon dioxide laser has been used for the first time to change the cartilage's shape. After the laser irradiation the cartilage has the tendency to retain its new form. Different types of laser modified cartilage structures were studied. The inferred physical mechanism for cartilage shaping using the stresses relaxation process is presented. The clinical significance of the results for corrective laser surgery is discussed.

  13. Tunable semiconductor lasers

    NASA Technical Reports Server (NTRS)

    Taghavi-Larigani, Shervin (Inventor); Vanzyl, Jakob J. (Inventor); Yariv, Amnon (Inventor)

    2006-01-01

    Tunable semiconductor lasers are disclosed requiring minimized coupling regions. Multiple laser embodiments employ ring resonators or ring resonator pairs using only a single coupling region with the gain medium are detailed. Tuning can be performed by changing the phase of the coupling coefficient between the gain medium and a ring resonator of the laser. Another embodiment provides a tunable laser including two Mach-Zehnder interferometers in series and a reflector coupled to a gain medium.

  14. Short wavelength laser

    DOEpatents

    Hagelstein, Peter L.

    1986-01-01

    A short wavelength laser (28) is provided that is driven by conventional-laser pulses (30, 31). A multiplicity of panels (32), mounted on substrates (34), are supported in two separated and alternately staggered facing and parallel arrays disposed along an approximately linear path (42). When the panels (32) are illuminated by the conventional-laser pulses (30, 31), single pass EUV or soft x-ray laser pulses (44, 46) are produced.

  15. Laser cutting system

    SciTech Connect

    Dougherty, Thomas J

    2015-03-03

    A workpiece cutting apparatus includes a laser source, a first suction system, and a first finger configured to guide a workpiece as it moves past the laser source. The first finger includes a first end provided adjacent a point where a laser from the laser source cuts the workpiece, and the first end of the first finger includes an aperture in fluid communication with the first suction system.

  16. Laser Assisted Microsurgical Anastomosis.

    DTIC Science & Technology

    1983-09-22

    Miami School of Medicine This Paper describes new experimental microsurgical procedures that * utilize laser infrared energy emitted at 10.6 um to...dioxide laser microsurgical technique takes advantage of the very high absorption of laser energy (at 10.6 um) by water in soft tissue to effect successful...describes a new surgical technique that utilizes laser heat energy to repair transected rat sciatic nerves, and nerve grafts. The energy emitted at

  17. Laser Detection of Pollution.

    ERIC Educational Resources Information Center

    Patel, C. K. N.

    1978-01-01

    Discusses the use of laser spectroscopy in determining the presence of specific gaseous constituents. Three of currently used modes for laser detection of pollution are reviewed; (1) long-path measurements; (2) laser raman (differential absorption) measurements; and (3) optoacoustic detection. (HM)

  18. Laser bottom hole assembly

    SciTech Connect

    Underwood, Lance D; Norton, Ryan J; McKay, Ryan P; Mesnard, David R; Fraze, Jason D; Zediker, Mark S; Faircloth, Brian O

    2014-01-14

    There is provided for laser bottom hole assembly for providing a high power laser beam having greater than 5 kW of power for a laser mechanical drilling process to advance a borehole. This assembly utilizes a reverse Moineau motor type power section and provides a self-regulating system that addresses fluid flows relating to motive force, cooling and removal of cuttings.

  19. Velocimetry with diode lasers

    NASA Astrophysics Data System (ADS)

    de Mul, F. F. M.; Jentink, H. W.; Koelink, M.; Greve, J.; Aarnoudse, J. G.

    The history of the application of diode lasers in velocimetry is reviewed. Some problems arising when using those lasers, e.g., mode hopping and wavelength shifts caused by temperature effects, are discussed, together with coherence effects encountered with diode lasers. The application in dual-beam velocimetry, in direct-contact velocimetry and in velocimetry using self-mixing will be discussed.

  20. Argon laser for otosclerosis

    NASA Astrophysics Data System (ADS)

    Michalski, Wojciech; Pospiech, Lucyna; Jankowska-Kuc, Malgorzata

    1995-03-01

    Up to now, among different kinds of lasers an argon laser is mostly used for otosclerosis. Exposure conditions at use of the laser beam are still not well defined. In order to achieve the optimum conditions a series of experiments has been made. Obtained results are presented in this paper.

  1. Laser power transmission

    NASA Technical Reports Server (NTRS)

    Conway, Edmund J.

    1992-01-01

    An overview of previous studies related to laser power transmission is presented. Particular attention is given to the use of solar pumped lasers for space power applications. Three general laser mechanisms are addressed: photodissociation lasing driven by sunlight, photoexcitation lasing driven directly by sunlight, and photoexcitation lasing driven by thermal radiation.

  2. LaserFest Celebration

    SciTech Connect

    Dr. Alan Chodos; Elizabeth A. Rogan

    2011-08-25

    LaserFest was the yearlong celebration, during 2010, of the 50th anniversary of the demonstration of the first working laser. The goals of LaserFest were: to highlight the impact of the laser in its manifold commercial, industrial and medical applications, and as a tool for ongoing scientific research; to use the laser as one example that illustrates, more generally, the route from scientific innovation to technological application; to use the laser as a vehicle for outreach, to stimulate interest among students and the public in aspects of physical science; to recognize and honor the pioneers who developed the laser and its many applications; to increase awareness among policymakers of the importance of R&D funding as evidenced by such technology as lasers. One way in which LaserFest sought to meet its goals was to encourage relevant activities at a local level all across the country -- and also abroad -- that would be identified with the larger purposes of the celebration and would carry the LaserFest name. Organizers were encouraged to record and advertise these events through a continually updated web-based calendar. Four projects were explicitly detailed in the proposals: 1) LaserFest on the Road; 2) Videos; 3) Educational material; and 4) Laser Days.

  3. Laser Fundamentals and Experiments.

    ERIC Educational Resources Information Center

    Van Pelt, W. F.; And Others

    As a result of work performed at the Southwestern Radiological Health Laboratory with respect to lasers, this manual was prepared in response to the increasing use of lasers in high schools and colleges. It is directed primarily toward the high school instructor who may use the text for a short course in laser fundamentals. The definition of the…

  4. Infrared diode laser spectroscopy

    NASA Astrophysics Data System (ADS)

    Civiš, S.; Cihelka, J.; Matulková, I.

    2010-12-01

    Three types of lasers (double-heterostructure 66 K InAsSb/InAsSbP laser diode, room temperature, multi quantum wells with distributed feedback (MQW with DFB) (GaInAsSb/AlGaAsSb based) diode laser and vertical cavity surface emitting lasers (VCSELs) (GaSb based) have been characterized using Fourier transform emission spectroscopy and compared. The photoacoustic technique was employed to determine the detection limit of formaldehyde (less than 1 ppmV) for the strongest absorption line of the v3 + v5 band in the emission region of the GaInAsSb/AlGaAsSb diode laser. The detection limit (less than 10 ppbV) of formaldehyde was achieved in the 2820 cm-1 spectral range in case of InAsSb/InAsSbP laser (fundamental bands of v1, v5). Laser sensitive detection (laser absorption together with high resolution Fourier transform infrared technique including direct laser linewidth measurement, infrared photoacoustic detection of neutral molecules (methane, form-aldehyde) is discussed. Additionally, very sensitive laser absorption techniques of such velocity modulation are discussed for case of laser application in laboratory research of molecular ions. Such sensitive techniques (originally developed for lasers) contributed very much in identifying laboratory microwave spectra of a series of anions (C6H-, C4H-, C2H-, CN-) and their discovery in the interstellar space (C6H-, C4H-).

  5. Laser Programs Highlights 1998

    SciTech Connect

    Lowdermilk, H.; Cassady, C.

    1999-12-01

    This report covers the following topics: Commentary; Laser Programs; Inertial Confinement Fusion/National Ignition Facility (ICF/NIF); Atomic Vapor Laser Isotope Separation (AVLIS); Laser Science and Technology (LS&T); Information Science and Technology Program (IS&T); Strategic Materials Applications Program (SMAP); Medical Technology Program (MTP) and Awards.

  6. Lasers for nonlinear microscopy.

    PubMed

    Wise, Frank

    2013-03-01

    Various versions of nonlinear microscopy are revolutionizing the life sciences, almost all of which are made possible because of the development of ultrafast lasers. In this article, the main properties and technical features of short-pulse lasers used in nonlinear microscopy are summarized. Recent research results on fiber lasers that will impact future instruments are also discussed.

  7. Polarization feedback laser stabilization

    DOEpatents

    Esherick, Peter; Owyoung, Adelbert

    1988-01-01

    A system for locking two Nd:YAG laser oscillators includes an optical path for feeding the output of one laser into the other with different polarizations. Elliptical polarization is incorporated into the optical path so that the change in polarization that occurs when the frequencies coincide may be detected to provide a feedback signal to control one laser relative to the other.

  8. Zeeman laser gyroscopes

    SciTech Connect

    Azarova, V V; Golyaev, Yu D; Saveliev, I I

    2015-02-28

    The history of invention and development of Zeeman laser gyroscopes, specific features of their optical scheme and operation principle are described. The construction and element base of modern laser angular velocity sensors with Zeeman-based frequency biasing are considered. The problems and prospects of their development are discussed. (laser gyroscopes)

  9. Excimer Lasers In Medicine

    NASA Astrophysics Data System (ADS)

    Tittel, Frank K.; Saidi, Iyad S.; Pettit, George H.; Wisoff, P. J.; Sauerbrey, Roland A.

    1989-06-01

    Excimer lasers emit light energy, short optical pulses at ultraviolet wavelengths, that results in a unique laser tissue interaction. This has led to an increasing number of studies into medical applications of these lasers in fields such as ophthalmology, urology, cardiology and neurology.

  10. Solar pumped laser

    NASA Technical Reports Server (NTRS)

    Lee, J. H.; Hohl, F.; Weaver, W. R. (Inventor)

    1984-01-01

    A solar pumped laser is described in which the lasant is a gas that will photodissociate and lase when subjected to sunrays. Sunrays are collected and directed onto the gas lasant to cause it to lase. Applications to laser propulsion and laser power transmission are discussed.

  11. Laser material processing system

    DOEpatents

    Dantus, Marcos

    2015-04-28

    A laser material processing system and method are provided. A further aspect of the present invention employs a laser for micromachining. In another aspect of the present invention, the system uses a hollow waveguide. In another aspect of the present invention, a laser beam pulse is given broad bandwidth for workpiece modification.

  12. Diode laser and endoscopic laser surgery.

    PubMed

    Sullins, Kenneth E

    2002-05-01

    Two functionally important differences exist between the diode laser and the carbon dioxide (CO2) laser (used more commonly in small animal surgery). Diode laser energy is delivered through a quartz fiber instead of being reflected through an articulated arm or waveguide. Quartz fibers are generally more flexible and resilient than waveguides and can be inserted through an endoscope for minimally invasive procedures. Laser-tissue interaction is the other significant difference. The CO2 laser is completely absorbed by water, which limits the effect to visible tissue. The diode wavelength is minimally absorbed by water and may affect tissue as deep as 10 mm below the surface in the free-beam mode. With proper respect for the tissue effect, these differences can be used to the advantage of the patient.

  13. Chalcogenide glass microsphere laser.

    PubMed

    Elliott, Gregor R; Murugan, G Senthil; Wilkinson, James S; Zervas, Michalis N; Hewak, Daniel W

    2010-12-06

    Laser action has been demonstrated in chalcogenide glass microsphere. A sub millimeter neodymium-doped gallium lanthanum sulphide glass sphere was pumped at 808 nm with a laser diode and single and multimode laser action demonstrated at wavelengths between 1075 and 1086 nm. The gallium lanthanum sulphide family of glass offer higher thermal stability compared to other chalcogenide glasses, and this, along with an optimized Q-factor for the microcavity allowed laser action to be achieved. When varying the pump power, changes in the output spectrum suggest nonlinear and/or thermal effects have a strong effect on laser action.

  14. Dual Wavelength Lasers

    NASA Technical Reports Server (NTRS)

    Walsh, Brian M.

    2010-01-01

    Dual wavelength lasers are discussed, covering fundamental aspects on the spectroscopy and laser dynamics of these systems. Results on Tm:Ho:Er:YAG dual wavelength laser action (Ho at 2.1 m and Er at 2.9 m) as well as Nd:YAG (1.06 and 1.3 m) are presented as examples of such dual wavelength systems. Dual wavelength lasers are not common, but there are criteria that govern their behavior. Based on experimental studies demonstrating simultaneous dual wavelength lasing, some general conclusions regarding the successful operation of multi-wavelength lasers can be made.

  15. Laser Diode Ignition (LDI)

    NASA Technical Reports Server (NTRS)

    Kass, William J.; Andrews, Larry A.; Boney, Craig M.; Chow, Weng W.; Clements, James W.; Merson, John A.; Salas, F. Jim; Williams, Randy J.; Hinkle, Lane R.

    1994-01-01

    This paper reviews the status of the Laser Diode Ignition (LDI) program at Sandia National Labs. One watt laser diodes have been characterized for use with a single explosive actuator. Extensive measurements of the effect of electrostatic discharge (ESD) pulses on the laser diode optical output have been made. Characterization of optical fiber and connectors over temperature has been done. Multiple laser diodes have been packaged to ignite multiple explosive devices and an eight element laser diode array has been recently tested by igniting eight explosive devices at predetermined 100 ms intervals.

  16. X-ray laser

    DOEpatents

    Nilsen, Joseph

    1991-01-01

    An X-ray laser (10) that lases between the K edges of carbon and oxygen, i.e. between 44 and 23 Angstroms, is provided. The laser comprises a silicon (12) and dysprosium (14) foil combination (16) that is driven by two beams (18, 20) of intense line focused (22, 24) optical laser radiation. Ground state nickel-like dysprosium ions (34) are resonantly photo-pumped to their upper X-ray laser state by line emission from hydrogen-like silicon ions (32). The novel X-ray laser should prove especially useful for the microscopy of biological specimens.

  17. Laser assisted deposition

    NASA Technical Reports Server (NTRS)

    Dutta, S.

    1983-01-01

    Applications of laser-based processing techniques to solar cell metallization are discussed. Laser-assisted thermal or photolytic maskless deposition from organometallic vapors or solutions may provide a viable alternative to photovoltaic metallization systems currently in use. High power, defocused excimer lasers may be used in conjunction with masks as an alternative to direct laser writing to provide higher throughput. Repeated pulsing with excimer lasers may eliminate the need for secondary plating techniques for metal film buildup. A comparison between the thermal and photochemical deposition processes is made.

  18. Stabilized Zeeman split laser

    NASA Technical Reports Server (NTRS)

    1981-01-01

    The development of a stablized Zeeman split laser for use in a polarization profilometer is discussed. A Hewlett-Packard laser was modified to stabilize the Zeeman split beat frequency thereby increasing the phase measurement accuracy from the Hewlett-Packard 3 degrees to an accuracy of .01 degrees. The addition of a two layered inductive winding converts the laser to a current controlled oscillator whose frequency is linearly related to coil current. This linear relationship between coil current and laser frequency permits phase locking the laser frequency to a stable crystal controlled reference frequency. The stability of the system is examined and the equipment operation procedures are outlined.

  19. Lasers in otorhinolaryngology

    NASA Astrophysics Data System (ADS)

    Pais Clemente, Manuel P.

    1992-03-01

    Lasers are now commonly accepted and widely used surgical instruments in otorhinolaryngology. There have been a great number of technological advances with lasers that have contributed to the expansion of this new surgical modality with an increased number of medical applications. Surgical strategies have also changed and are more favorable toward conservative surgery in which less tissues is removed than with more radical resections. This combination of improving technology and medical attitudes has changed the field of otorhinolaryngology, and resulted in an expanding use of laser surgery. Since 1973 we have been using the carbon dioxide laser in the treatment of diseases of the upper aero digestive systems, learning this new surgical technique from the pioneer work of Strong, Jako, and Vaughan. It is our conviction that a laser surgeon must have a thorough knowledge of laser biophysics, instrumentation, safety protocols, and surgical indications, and have the technical skills to perform laser surgery. Laser technology continues to improve at an increased speed, and it is imperative to update knowledge of current and potential applications of lasers in our specialty. It is the purpose of this article to present our clinical experience of 18 years with the use of lasers in surgery of ORL, emphasizing the carbon dioxide laser.

  20. Laser surgery: using the carbon dioxide laser.

    PubMed Central

    Wright, V. C.

    1982-01-01

    In 1917 Einstein theorized tha through an atomic process a unique kind of electromagnetic radiation could be produced by stimulated emission. When such radiation is in the optical or infrared spectrum it is termed laser (light amplification by stimulated emission of radiation) light. A laser, a high-intensity light source, emits a nearly parallel electromagnetic beam of energy at a given wavelength that can be captured by a lens and concentrated in the focal spot. The wavelength determines how the laser will be used. The carbon dioxide laser is now successfully employed for some surgical procedures in gynecology, otorhinolaryngology, neurosurgery, and plastic and general surgery. The CO2 laser beam is directed through the viewing system of an operating microscope or through a hand-held laser component. Its basic action in tissue is thermal vaporization; it causes minimal damage to adjacent tissues. Surgeons require special training in the basic methods and techniques of laser surgery, as well as in the safety standards that must be observed. Images FIG. 5 PMID:7074503

  1. Laser Synchrotron Source (LSS)

    NASA Astrophysics Data System (ADS)

    Sprangle, Philip; Ting, Antonio; Esarey, Eric; Fisher, Amon; Mourou, Gerald

    1993-02-01

    The Laser Synchrotron Source (LSS) utilizes a high peak power or high average power laser to generate within a vacuum chamber a laser beam travelling in one direction to interact with an electron beam traveling in an opposite direction in order to generate high-power x-rays. A ring resonator formed by a plurality of mirrors directs the laser beam in a closed loop to impact with the electron beam to produce x-rays. Concave mirrors in the ring resonator focus the laser beam upon the point where the laser beam interacts with the electron beam to intensify the laser energy at that point. When a Radio Frequency Linear Accelerator (RF linac) is used to produce the electron beam, x-rays having a short pulse length are generated. When a betatron is used as an electron source, x-rays having a long pulse length are generated.

  2. Laser safety in dentistry

    NASA Astrophysics Data System (ADS)

    Wigdor, Harvey A.

    1997-05-01

    One of the major causes of anxiety in the dental clinic is the dental handpiece. Because dentists wish to provide a method which can replace the drill there has often been a premature use of the laser in dentistry. Various lasers have been introduced into the clinic before research has shown the laser used is of clinical benefit. Any new treatment method must not compromise the health of the patient being treated. Thus a method of evaluating the clinical abilities of dentists and their understanding the limitations of the laser used must be developed. Dentist must be trained in the basic interaction of the laser on oral tissues. The training has to concentrate on the variation of the laser wavelength absorption in the different tissues of the oral cavity. Because of the differences in the optical properties of these tissues great care must be exercised by practitioners using lasers on patients.

  3. Laser Applications in Orthodontics

    PubMed Central

    Heidari, Somayeh; Torkan, Sepideh

    2013-01-01

    A laser is a collimated single wavelength of light which delivers a concentrated source of energy. Soon after different types of lasers were invented, investigators began to examine the effects of different wavelengths of laser energy on oral tissues, routine dental procedures and experimental applications. Orthodontists, along with other specialist in different fields of dentistry, can now benefit from several different advantages that lasers provide during the treatment process, from the beginning of the treatment, when separators are placed, to the time of resin residues removal from the tooth surface at the end of orthodontic treatment. This article outlines some of the most common usages of laser beam in orthodontics and also provides a comparison between laser and other conventional method that were the standard of care prior to the advent of laser in this field. PMID:25606324

  4. Lasers in orthodontics

    PubMed Central

    Nalcaci, Ruhi; Cokakoglu, Serpil

    2013-01-01

    Many types of dental lasers are currently available that can be efficiently used for soft and hard tissue applications in the field of orthodontics. For achieving the desired effects in the target tissue, knowledge of laser characteristics such as power, wavelength and timing, is necessary. Laser therapy is advantageous because it often avoids bleeding, can be pain free, is non-invasive and is relatively quick. The high cost is its primary disadvantage. It is very important to take the necessary precautions to prevent possible tissue damage when using laser dental systems. Here, we reviewed the main types and characteristics of laser systems used in dental practice and discuss the applications of lasers in orthodontics, harmful effects and laser system safety. PMID:24966719

  5. Raman fiber lasers

    NASA Astrophysics Data System (ADS)

    Supradeepa, V. R.; Feng, Yan; Nicholson, Jeffrey W.

    2017-02-01

    High-power fiber lasers have seen tremendous development in the last decade, with output powers exceeding multiple kilowatts from a single fiber. Ytterbium has been at the forefront as the primary rare-earth-doped gain medium owing to its inherent material advantages. However, for this reason, the lasers are largely confined to the narrow emission wavelength region of ytterbium. Power scaling at other wavelength regions has lagged significantly, and a large number of applications rely upon the diversity of emission wavelengths. Currently, Raman fiber lasers are the only known wavelength agile, scalable, high-power fiber laser technology that can span the wavelength spectrum. In this review, we address the technology of Raman fiber lasers, specifically focused on the most recent developments. We will also discuss several applications of Raman fiber lasers in laser pumping, frequency conversion, optical communications and biology.

  6. Lasers in periodontology.

    PubMed

    Mavrogiannis, M; Thomason, J M; Seymour, R A

    2004-11-01

    Since the development of the ruby laser by Maiman in 1960, lasers have been widely employed in medicine for a number of years. The purpose of this paper is to summarize potential applications for lasers in dentistry, with special regard to periodontology. This article briefly describes clinical applications of lasers and laser safety. Particularly, the use of a diode laser seems to be promising, especially in already compromised transplant patients, who need to be treated with a technique where the operative and post-operative blood loss, post-operative discomfort and the recurrence of drug-induced gingival overgrowth need to be kept to a minimum or eliminated. Therefore, the use of lasers in periodontology may lead to an alteration in present clinical practice and help to establish the best management strategy because, by maintaining periodontal health, the life quality of patients can be improved.

  7. Lasers in dentistry

    NASA Astrophysics Data System (ADS)

    Keller, Ulrich

    1991-11-01

    The infrared-laser systems like the Er:YAG, the cw CO2, the Nd:YAG, and the UV- excimer lasers are being investigated for preparing tooth-hard substances. The infrared lasers cause thermal damage to the enamel, the dentin, and the pulp with the exception of the Er:YAG laser. No thermal damage occurs using the Er:YAG laser under practical conditions because of the special thermomechanical ablation process. The ablation rates of the UV- excimer lasers are to low for practical use. Enhancing the ablation efficiency by high- repetition rates causes thermal side effects to occur. Therefore, only the Er:YAG laser has the potential to partially replace the mechanical drill.

  8. Semiconductor nanowire lasers

    NASA Astrophysics Data System (ADS)

    Eaton, Samuel W.; Fu, Anthony; Wong, Andrew B.; Ning, Cun-Zheng; Yang, Peidong

    2016-06-01

    The discovery and continued development of the laser has revolutionized both science and industry. The advent of miniaturized, semiconductor lasers has made this technology an integral part of everyday life. Exciting research continues with a new focus on nanowire lasers because of their great potential in the field of optoelectronics. In this Review, we explore the latest advancements in the development of nanowire lasers and offer our perspective on future improvements and trends. We discuss fundamental material considerations and the latest, most effective materials for nanowire lasers. A discussion of novel cavity designs and amplification methods is followed by some of the latest work on surface plasmon polariton nanowire lasers. Finally, exciting new reports of electrically pumped nanowire lasers with the potential for integrated optoelectronic applications are described.

  9. Nanofabrication with pulsed lasers.

    PubMed

    Kabashin, Av; Delaporte, Ph; Pereira, A; Grojo, D; Torres, R; Sarnet, Th; Sentis, M

    2010-02-24

    An overview of pulsed laser-assisted methods for nanofabrication, which are currently developed in our Institute (LP3), is presented. The methods compass a variety of possibilities for material nanostructuring offered by laser-matter interactions and imply either the nanostructuring of the laser-illuminated surface itself, as in cases of direct laser ablation or laser plasma-assisted treatment of semiconductors to form light-absorbing and light-emitting nano-architectures, as well as periodic nanoarrays, or laser-assisted production of nanoclusters and their controlled growth in gaseous or liquid medium to form nanostructured films or colloidal nanoparticles. Nanomaterials synthesized by laser-assisted methods have a variety of unique properties, not reproducible by any other route, and are of importance for photovoltaics, optoelectronics, biological sensing, imaging and therapeutics.

  10. Space qualified laser sources

    NASA Astrophysics Data System (ADS)

    Heine, Frank; Schwander, Thomas; Lange, Robert; Smutny, Berry

    2006-04-01

    Tesat-Spacecom has developed a series of fiber coupled single frequency lasers for space applications ranging from onboard metrology for space borne FTIR spectrometers to step tunable seed lasers for LIDAR applications. The cw-seed laser developed for the ESA AEOLUS Mission shows a 3* 10 -11 Allen variance from 1 sec time intervals up to 1000 sec. Q-switched lasers with stable beam pointing under space environments are another field of development. One important aspect of a space borne laser system is a reliable fiber coupled laser diode pump source around 808nm. A dedicated development concerning chip design and packaging yielded in a 5*10 6h MTTF (mean time to failure) for the broad area emitters. Qualification and performance test results for the different laser assemblies will be presented and their application in the different space programs.

  11. Lasers in oral surgery

    NASA Astrophysics Data System (ADS)

    Keller, Ulrich; Hibst, Raimund

    1994-12-01

    The indications of lasers in oral surgery are defined by the laser-tissue interaction types. These are mainly thermal effects depending especially on the absorption of laser light in varying biological tissues. In histological sections different laser effects are demonstrated on oral mucosa, bone and cartilage, which have a great influence on wound healing and subsequently on clinical indications of the different wavelengths. On the one hand the good coagulation effect of the Nd:YAG laser is wanted for hemostasis in soft tissue surgery. On the other hand, for the treatment of precancerous dysplasias or neoplasias an effective cutting with a coagulation effect like using the CO2 laser is necessary. However, the excision of benign mucosal lesions as well as performing osteotomies or shaping of cartilage should be undertaken with the Er:YAG laser without greater coagulation and consequently without any delay of wound healing.

  12. Micromachining with copper lasers

    NASA Astrophysics Data System (ADS)

    Knowles, Martyn R. H.; Bell, Andy; Foster-Turner, Gideon; Rutterford, Graham; Chudzicki, J.; Kearsley, Andrew J.

    1997-04-01

    In recent years the copper laser has undergone extensive development and has emerged as a leading and unique laser for micromachining. The copper laser is a high average power (10 - 250 W), high pulse repetition rate (2 - 32 kHz), visible laser (511 nm and 578 nm) that produces high peak power (typically 200 kW), short pulses (30 ns) and very good beam quality (diffraction limited). This unique set of laser parameters results in exceptional micro-machining in a wide variety of materials. Typical examples of the capabilities of the copper laser include the drilling of small holes (10 - 200 micrometer diameter) in materials as diverse as steel, ceramic, diamond and polyimide with micron precision and low taper (less than 1 degree) cutting and profiling of diamond. Application of the copper laser covers the electronic, aerospace, automotive, nuclear, medical and precision engineering industries.

  13. ORION laser target diagnostics.

    PubMed

    Bentley, C D; Edwards, R D; Andrew, J E; James, S F; Gardner, M D; Comley, A J; Vaughan, K; Horsfield, C J; Rubery, M S; Rothman, S D; Daykin, S; Masoero, S J; Palmer, J B; Meadowcroft, A L; Williams, B M; Gumbrell, E T; Fyrth, J D; Brown, C R D; Hill, M P; Oades, K; Wright, M J; Hood, B A; Kemshall, P

    2012-10-01

    The ORION laser facility is one of the UK's premier laser facilities which became operational at AWE in 2010. Its primary mission is one of stockpile stewardship, ORION will extend the UK's experimental plasma physics capability to the high temperature, high density regime relevant to Atomic Weapons Establishment's (AWE) program. The ORION laser combines ten laser beams operating in the ns regime with two sub ps short pulse chirped pulse amplification beams. This gives the UK a unique combined long pulse/short pulse laser capability which is not only available to AWE personnel but also gives access to our international partners and visiting UK academia. The ORION laser facility is equipped with a comprehensive suite of some 45 diagnostics covering optical, particle, and x-ray diagnostics all able to image the laser target interaction point. This paper focuses on a small selection of these diagnostics.

  14. Lasers in space

    NASA Astrophysics Data System (ADS)

    Michaelis, M. M.; Forbes, A.; Bingham, R.; Kellett, B. J.; Mathye, A.

    2008-05-01

    A variety of laser applications in space, past, present, future and far future are reviewed together with the contributions of some of the scientists and engineers involved, especially those that happen to have South African connections. Historically, two of the earliest laser applications in space, were atmospheric LIDAR and lunar ranging. These applications involved atmospheric physicists, several astronauts and many of the staff recruited into the Soviet and North American lunar exploration programmes. There is a strong interest in South Africa in both LIDAR and lunar ranging. Shortly after the birth of the laser (and even just prior) theoretical work on photonic propulsion and space propulsion by laser ablation was initiated by Georgii Marx, Arthur Kantrowitz and Eugen Saenger. Present or near future experimental programs are developing in the following fields: laser ablation propulsion, possibly coupled with rail gun or gas gun propulsion; interplanetary laser transmission; laser altimetry; gravity wave detection by space based Michelson interferometry; the de-orbiting of space debris by high power lasers; atom laser interferometry in space. Far future applications of laser-photonic space-propulsion were also pioneered by Carl Sagan and Robert Forward. They envisaged means of putting Saenger's ideas into practice. Forward also invented a laser based method for manufacturing solid antimatter or SANTIM, well before the ongoing experiments at CERN with anti-hydrogen production and laser-trapping. SANTIM would be an ideal propellant for interstellar missions if it could be manufactured in sufficient quantities. It would be equally useful as a power source for the transmission of information over light year distances. We briefly mention military lasers. Last but not least, we address naturally occurring lasers in space and pose the question: "did the Big Bang lase?"

  15. Laser system using ultra-short laser pulses

    DOEpatents

    Dantus, Marcos; Lozovoy, Vadim V.; Comstock, Matthew

    2009-10-27

    A laser system using ultrashort laser pulses is provided. In another aspect of the present invention, the system includes a laser, pulse shaper and detection device. A further aspect of the present invention employs a femtosecond laser and binary pulse shaping (BPS). Still another aspect of the present invention uses a laser beam pulse, a pulse shaper and a SHG crystal.

  16. Frequency comb swept lasers

    PubMed Central

    Tsai, Tsung-Han; Zhou, Chao; Adler, Desmond C.; Fujimoto, James G.

    2010-01-01

    We demonstrate a frequency comb (FC) swept laser and a frequency comb Fourier domain mode locked (FC-FDML) laser for applications in optical coherence tomography (OCT). The fiber-based FC swept lasers operate at a sweep rate of 1kHz and 120kHz, respectively over a 135nm tuning range centered at 1310nm with average output powers of 50mW. A 25GHz free spectral range frequency comb filter in the swept lasers causes the lasers to generate a series of well defined frequency steps. The narrow bandwidth (0.015nm) of the frequency comb filter enables a ~−1.2dB sensitivity roll off over ~3mm range, compared to conventional swept source and FDML lasers which have −10dB and −5dB roll offs, respectively. Measurements at very long ranges are possible with minimal sensitivity loss, however reflections from outside the principal measurement range of 0–3mm appear aliased back into the principal range. In addition, the frequency comb output from the lasers are equally spaced in frequency (linear in k-space). The filtered laser output can be used to self-clock the OCT interference signal sampling, enabling direct fast Fourier transformation of the fringe signals, without the need for fringe recalibration procedures. The design and operation principles of FC swept lasers are discussed and designs for short cavity lasers for OCT and interferometric measurement applications are proposed. PMID:19997365

  17. Laser treatment in gynecology

    NASA Astrophysics Data System (ADS)

    de Riese, Cornelia

    2004-07-01

    This presentation is designed as a brief overview of laser use in gynecology, for non-medical researchers involved in development of new laser techniques. The literature of the past decade is reviewed. Differences in penetration, absorption, and suitable delivery media for the beams dictate clinical application. The use of CO2 laser in the treatment of uterine cervical intraepithelial lesions is well established and indications as well as techniques have not changed over 30 years. The Cochrane Systematic Review from 2000 suggests no obviously superior technique. CO2 laser ablation of the vagina is also established as a safe treatment modality for VAIN. CO2 laser permits treatment of lesions with excellent cosmetic and functional results. The treatment of heavy menstrual bleeding by destruction of the endometrial lining using various techniques has been the subject of a 2002 Cochran Database Review. Among the compared treatment modalities are newer and modified laser techniques. Conclusion by reviewers is that outcomes and complication profiles of newer techniques compare favorably with the gold standard of endometrial resection. The ELITT diode laser system is one of the new successful additions. CO2 laser is also the dominant laser type used with laparoscopy for ablation of endometriotic implants. Myoma coagulation or myolysis with Nd:Yag laser through the laparoscope or hysteroscope is a conservative treatment option. Even MRI guided percutaneous approaches have been described. No long-term data are available.

  18. Photobiomodulation in laser surgery

    NASA Astrophysics Data System (ADS)

    Liu, Timon Cheng-Yi; Rong, Dong-Liang; Huang, Jin; Deng, Xiao-Yuan; Liu, Song-Hao

    2006-01-01

    Laser surgery provides good exposure with clear operating fields and satisfactory preliminary functional results. In contrast to conventional excision, it was found that matrix metalloproteinases and the tissue inhibitors of metalloproteinases -1 mRNA expression is higher, myofibroblasts appeared and disappeared slower in laser excision wounds. It has been suggested that the better anatomical and functional results achieved following laser cordectomy may be explained by the fact that such procedures result in better, more rapid healing processes to recover vocal cord for early glottic tumors and better. In this paper, the role of photobiomodulation in laser surgery will be discussed by the cultured monolayer normal human skin fibroblast model of the photobiomodulation of marginal irradiation of high intensity laser beam, the photobiomodulation related to the irradiated tissue, the biological information model of photobiomodulation and the animal models of laser surgery. Although high intensity laser beam is so intense that it destroys the irradiated cells or tissue, its marginal irradiation intensity is so low that there is photobiomodulation on non-damage cells to modulate the regeneration of partly damaged tissue so that the surgery of laser of different parameters results in different post-surgical recovery. It was concluded that photobiomodulation might play an important role in the long-term effects of laser surgery, which might be used to design laser surgery.

  19. Frequency comb swept lasers.

    PubMed

    Tsai, Tsung-Han; Zhou, Chao; Adler, Desmond C; Fujimoto, James G

    2009-11-09

    We demonstrate a frequency comb (FC) swept laser and a frequency comb Fourier domain mode locked (FC-FDML) laser for applications in optical coherence tomography (OCT). The fiber-based FC swept lasers operate at a sweep rate of 1kHz and 120kHz, respectively over a 135nm tuning range centered at 1310nm with average output powers of 50mW. A 25GHz free spectral range frequency comb filter in the swept lasers causes the lasers to generate a series of well defined frequency steps. The narrow bandwidth (0.015nm) of the frequency comb filter enables a approximately -1.2dB sensitivity roll off over approximately 3mm range, compared to conventional swept source and FDML lasers which have -10dB and -5dB roll offs, respectively. Measurements at very long ranges are possible with minimal sensitivity loss, however reflections from outside the principal measurement range of 0-3mm appear aliased back into the principal range. In addition, the frequency comb output from the lasers are equally spaced in frequency (linear in k-space). The filtered laser output can be used to self-clock the OCT interference signal sampling, enabling direct fast Fourier transformation of the fringe signals, without the need for fringe recalibration procedures. The design and operation principles of FC swept lasers are discussed and designs for short cavity lasers for OCT and interferometric measurement applications are proposed.

  20. Lasers in medicine

    NASA Astrophysics Data System (ADS)

    Peng, Qian; Juzeniene, Asta; Chen, Jiyao; Svaasand, Lars O.; Warloe, Trond; Giercksky, Karl-Erik; Moan, Johan

    2008-05-01

    It is hard to imagine that a narrow, one-way, coherent, moving, amplified beam of light fired by excited atoms is powerful enough to slice through steel. In 1917, Albert Einstein speculated that under certain conditions atoms could absorb light and be stimulated to shed their borrowed energy. Charles Townes coined the term laser (light amplification by stimulated emission of radiation) in 1951. Theodore Maiman investigated the glare of a flash lamp in a rod of synthetic ruby, creating the first human-made laser in 1960. The laser involves exciting atoms and passing them through a medium such as crystal, gas or liquid. As the cascade of photon energy sweeps through the medium, bouncing off mirrors, it is reflected back and forth, and gains energy to produce a high wattage beam of light. Although lasers are today used by a large variety of professions, one of the most meaningful applications of laser technology has been through its use in medicine. Being faster and less invasive with a high precision, lasers have penetrated into most medical disciplines during the last half century including dermatology, ophthalmology, dentistry, otolaryngology, gastroenterology, urology, gynaecology, cardiology, neurosurgery and orthopaedics. In many ways the laser has revolutionized the diagnosis and treatment of a disease. As a surgical tool the laser is capable of three basic functions. When focused on a point it can cauterize deeply as it cuts, reducing the surgical trauma caused by a knife. It can vaporize the surface of a tissue. Or, through optical fibres, it can permit a doctor to see inside the body. Lasers have also become an indispensable tool in biological applications from high-resolution microscopy to subcellular nanosurgery. Indeed, medical lasers are a prime example of how the movement of an idea can truly change the medical world. This review will survey various applications of lasers in medicine including four major categories: types of lasers, laser

  1. Anterior segment optical coherence tomography evaluation of corneal epithelium healing time after 2 different surface ablation methods

    PubMed Central

    Eliaçik, Mustafa; Bayramlar, Hüseyin; Erdur, Sevil K.; Karabela, Yunus; Demirci, Göktuğ; Gülkilik, İbrahim G.; Özsütçü, Mustafa

    2015-01-01

    Objectives: To compare epithelial healing time following laser epithelial keratomileusis (LASEK) and photorefractive keratectomy (PRK) with anterior segment optic coherence tomography (AS-OCT). Methods: This prospective interventional case series study comprised 56 eyes of 28 patients that underwent laser refractive surgery in the Department of Ophthalmology, Medipol University Medical Faculty, Istanbul, Turkey, between March 2014 and May 2014. Each patient was randomized to have one eye operated on with PRK, and the other with LASEK. Patients were examined daily for 5 days, and epithelial healing time was assessed by using AS-OCT without removing therapeutic contact lens (TCL). Average discomfort scores were calculated from ratings obtained from questions regarding pain, photophobia, and lacrimation according to a scale of 0 (none) to 5. Results: The mean re-epithelialization time assessed with AS-OCT was 3.07±0.64 days in the PRK group, 3.55±0.54 days in the LASEK group, and the difference was statistically significant (p=0.03). Mean subjective discomfort score was 4.42±0.50 in the PRK eyes, and 2.85±0.44 in the LASEK eyes on the first exam day (p=0.001). The score obtained on the second (p=0.024), and third day (p=0.03) were also statistically significant. The fourth (p=0.069), and fifth days scores (p=0.1) showed no statistically significant difference between groups. Conclusion: The PRK showed a statistically significant shorter epithelial healing time, but had a statistically significant higher discomfort score until the postoperative fourth day compared with LASEK. PMID:25630007

  2. EBM regeneration and changes in EBM component mRNA expression in stromal cells after corneal injury

    PubMed Central

    Santhanam, Abirami; Marino, Gustavo K.; Torricelli, Andre A. M.

    2017-01-01

    Purpose To investigate the production of the epithelial basement membrane (EBM) component mRNAs at time points before lamina lucida and lamina densa regeneration in anterior stromal cells after corneal injury that would heal with and without fibrosis. Methods Rabbit corneas were removed from 2 to 19 days after −4.5D or −9.0D photorefractive keratectomy (PRK) with the VISX S4 IR laser. Corneas were evaluated with transmission electron microscopy (TEM) for full regeneration of the lamina lucida and the lamina densa. Laser capture microdissection (LCM) based quantitative real-time (RT)–PCR was used to quantitate the expression of mRNAs for laminin α-3 (LAMA3), perlecan, nidogen-1, and nidogen-2 in the anterior stroma. Results After −4.5D PRK, EBM was found to be fully regenerated at 8 to 10 days after surgery. At 4 days after PRK, the nidogen-2 and LAMA3 mRNAs levels were detected at statistically significantly lower levels in the anterior stroma of the −9.0D PRK corneas (where the EBM would not fully regenerate) compared to the −4.5D PRK corneas (where the EBM was destined to fully regenerate). At 7 days after PRK, nidogen-2 and LAMA3 mRNAs continued to be statistically significantly lower in the anterior stroma of the −9.0D PRK corneas compared to their expression in the anterior stroma of the −4.5D PRK corneas. Conclusions Key EBM components LAMA3 and nidogen-2 mRNAs are expressed at higher levels in the anterior stroma during EBM regeneration in the −4.5D PRK corneas where the EBM is destined to fully regenerate and no haze developed compared to the −9.0D PRK corneas where the EBM will not fully regenerate and myofibroblast-related stromal fibrosis (haze) will develop. PMID:28275314

  3. Laser Safety Inspection Criteria

    SciTech Connect

    Barat, K

    2005-02-11

    A responsibility of the Laser Safety Officer (LSO) is to perform laser safety audits. The American National Standard Z136.1 Safe use of Lasers references this requirement in several sections: (1) Section 1.3.2 LSO Specific Responsibilities states under Hazard Evaluation, ''The LSO shall be responsible for hazards evaluation of laser work areas''; (2) Section 1.3.2.8, Safety Features Audits, ''The LSO shall ensure that the safety features of the laser installation facilities and laser equipment are audited periodically to assure proper operation''; and (3) Appendix D, under Survey and Inspections, it states, ''the LSO will survey by inspection, as considered necessary, all areas where laser equipment is used''. Therefore, for facilities using Class 3B and or Class 4 lasers, audits for laser safety compliance are expected to be conducted. The composition, frequency and rigueur of that inspection/audit rests in the hands of the LSO. A common practice for institutions is to develop laser audit checklists or survey forms. In many institutions, a sole Laser Safety Officer (LSO) or a number of Deputy LSO's perform these audits. For that matter, there are institutions that request users to perform a self-assessment audit. Many items on the common audit list and the associated findings are subjective because they are based on the experience and interest of the LSO or auditor in particular items on the checklist. Beam block usage is an example; to one set of eyes a particular arrangement might be completely adequate, while to another the installation may be inadequate. In order to provide more consistency, the National Ignition Facility Directorate at Lawrence Livermore National Laboratory (NIF-LLNL) has established criteria for a number of items found on the typical laser safety audit form. These criteria are distributed to laser users, and they serve two broad purposes: first, it gives the user an expectation of what will be reviewed by an auditor, and second, it is an

  4. Laser materials production

    NASA Astrophysics Data System (ADS)

    Gianinoni, I.; Musci, M.

    1985-09-01

    The characteristics and the perspectives of the new photochemical laser techniques for materials production will be briefly analysed and some recent experimental results both on large area deposition of thin films and on synthesis of powders will be reported. As an example of an IR laser process, the cw CO 2 laser-induced deposition of hydrogenated amorphous silicon will be described in some detail. The results of some UV experiments for semiconductor, metal and insulating film depositions will also be discussed. The features of the process for laser-driven synthesis of powders and the characteristics of the produced particles will be evidenced, and some of their technological applications will be outlined. The requirements of the laser sources suitable for this kind of applications are in general the same as in gas-phase laser chemistry, however it will be pointed out how some parameters are more significant for this specific use.

  5. Pulsed excimer laser processing

    NASA Technical Reports Server (NTRS)

    Wong, D.

    1985-01-01

    The status of pulsed excimer laser processing of PV cells is presented. The cost effective feasibility of fabricating high efficiency solar cells on Czochralski wafers using a pulsed excimer laser for junction formation, surface passivation, and front metallization. Laser annealing results were promising with the best AR coated cell having an efficiency of 16.1%. Better results would be expected with larger laser spot size because there was some degradation in open circuit voltage caused by laser spot overlap and edge effects. Surface heating and photolytic decomposition by the laser was used to deposit tungsten from the reaction of tungsten hexafluoride and hydrogen. The line widths were 5 to 10 mils, and the depositions passed the tape adhesion test. Thinner lines are practical using an optimized optical system.

  6. Pulsed excimer laser processing

    NASA Astrophysics Data System (ADS)

    Wong, D.

    1985-06-01

    The status of pulsed excimer laser processing of PV cells is presented. The cost effective feasibility of fabricating high efficiency solar cells on Czochralski wafers using a pulsed excimer laser for junction formation, surface passivation, and front metallization. Laser annealing results were promising with the best AR coated cell having an efficiency of 16.1%. Better results would be expected with larger laser spot size because there was some degradation in open circuit voltage caused by laser spot overlap and edge effects. Surface heating and photolytic decomposition by the laser was used to deposit tungsten from the reaction of tungsten hexafluoride and hydrogen. The line widths were 5 to 10 mils, and the depositions passed the tape adhesion test. Thinner lines are practical using an optimized optical system.

  7. Laser/tissue interaction.

    PubMed

    Dederich, D N

    1991-01-01

    When laser light impinges on tissue, it can reflect, scatter, be absorbed, or transmit to the surrounding tissue. Absorption controls to a great degree the extent to which reflection, scattering and transmission occur, and wavelength is the primary determinant of absorption. The CO2 laser is consistently absorbed by most materials and tissues and the Nd-YAG laser wavelength is preferentially absorbed in pigmented tissues. The factors which determine the initial tissue effect include the laser wavelength, laser power, laser waveform, tissue optical properties, and tissue thermal properties. There are almost an infinite number of combinations of these factors possible, many of which would result in unacceptable damage to the tissues. This underscores the need to thoroughly test any particular combination of these factors on the conceptual, in-vitro, and in-vivo level before a treatment is offered.

  8. Photonic Crystal Microchip Laser.

    PubMed

    Gailevicius, Darius; Koliadenko, Volodymyr; Purlys, Vytautas; Peckus, Martynas; Taranenko, Victor; Staliunas, Kestutis

    2016-09-29

    The microchip lasers, being very compact and efficient sources of coherent light, suffer from one serious drawback: low spatial quality of the beam strongly reducing the brightness of emitted radiation. Attempts to improve the beam quality, such as pump-beam guiding, external feedback, either strongly reduce the emission power, or drastically increase the size and complexity of the lasers. Here it is proposed that specially designed photonic crystal in the cavity of a microchip laser, can significantly improve the beam quality. Experiments show that a microchip laser, due to spatial filtering functionality of intracavity photonic crystal, improves the beam quality factor M(2) reducing it by a factor of 2, and increase the brightness of radiation by a factor of 3. This comprises a new kind of laser, the "photonic crystal microchip laser", a very compact and efficient light source emitting high spatial quality high brightness radiation.

  9. Synthetic laser medium

    DOEpatents

    Stokowski, S.E.

    1987-10-20

    A laser medium is particularly useful in high average power solid state lasers. The laser medium includes a chromium dopant and preferably neodymium ions as codopant, and is primarily a gadolinium scandium gallium garnet, or an analog thereof. Divalent cations inhibit spiral morphology as large boules from which the laser medium is derived are grown, and a source of ions convertible between a trivalent state and a tetravalent state at a low ionization energy are in the laser medium to reduce an absorption coefficient at about one micron wavelength otherwise caused by the divalent cations. These divalent cations and convertible ions are dispersed in the laser medium. Preferred convertible ions are provided from titanium or cerium sources.

  10. Synthetic laser medium

    DOEpatents

    Stokowski, Stanley E.

    1989-01-01

    A laser medium is particularly useful in high average power solid state lasers. The laser medium includes a chormium dopant and preferably neodymium ions as codopant, and is primarily a gadolinium scandium gallium garnet, or an analog thereof. Divalent cations inhibit spiral morphology as large boules from which the laser medium is derived are grown, and a source of ions convertible between a trivalent state and a tetravalent state at a low ionization energy are in the laser medium to reduce an absorption coefficient at about one micron wavelength otherwise caused by the divalent cations. These divalent cations and convertible ions are dispersed in the laser medium. Preferred convertible ions are provided from titanium or cerium sources.

  11. Nanofabrication with Pulsed Lasers

    PubMed Central

    2010-01-01

    An overview of pulsed laser-assisted methods for nanofabrication, which are currently developed in our Institute (LP3), is presented. The methods compass a variety of possibilities for material nanostructuring offered by laser–matter interactions and imply either the nanostructuring of the laser-illuminated surface itself, as in cases of direct laser ablation or laser plasma-assisted treatment of semiconductors to form light-absorbing and light-emitting nano-architectures, as well as periodic nanoarrays, or laser-assisted production of nanoclusters and their controlled growth in gaseous or liquid medium to form nanostructured films or colloidal nanoparticles. Nanomaterials synthesized by laser-assisted methods have a variety of unique properties, not reproducible by any other route, and are of importance for photovoltaics, optoelectronics, biological sensing, imaging and therapeutics. PMID:20672069

  12. Laser rocket system analysis

    NASA Technical Reports Server (NTRS)

    Jones, W. S.; Forsyth, J. B.; Skratt, J. P.

    1979-01-01

    The laser rocket systems investigated in this study were for orbital transportation using space-based, ground-based and airborne laser transmitters. The propulsion unit of these systems utilizes a continuous wave (CW) laser beam focused into a thrust chamber which initiates a plasma in the hydrogen propellant, thus heating the propellant and providing thrust through a suitably designed nozzle and expansion skirt. The specific impulse is limited only by the ability to adequately cool the thruster and the amount of laser energy entering the engine. The results of the study showed that, with advanced technology, laser rocket systems with either a space- or ground-based laser transmitter could reduce the national budget allocated to space transportation by 10 to 345 billion dollars over a 10-year life cycle when compared to advanced chemical propulsion systems (LO2-LH2) of equal capability. The variation in savings depends upon the projected mission model.

  13. Micro-laser

    DOEpatents

    Hutchinson, Donald P.; Richards, Roger K.

    2003-07-22

    A micro-laser is disclosed which includes a waveguide, a first and a second subwavelength resonant grating in the waveguide, and at least one photonic band gap resonant structure (PBG) in the waveguide and at least one amplifying medium in the waveguide. PBG features are positioned between the first and second subwavelength resonant gratings and allow introduction of amplifying mediums into the highly resonant guided micro-laser microcavity. The micro-laser may be positioned on a die of a bulk substrate material with one or more electronic and optical devices and may be communicably connected to the same. A method for fabricating a micro-laser is disclosed. A method for tuning the micro-laser is also disclosed. The micro-laser may be used as an optical regenerator, or a light source for data transfer or for optical computing.

  14. Lasers in periodontics

    PubMed Central

    Elavarasu, Sugumari; Naveen, Devisree; Thangavelu, Arthiie

    2012-01-01

    Laser is one of the most captivating technologies in dental practice since Theodore Maiman in 1960 invented the ruby laser. Lasers in dentistry have revolutionized several areas of treatment in the last three and a half decades of the 20th century. Introduced as an alternative to mechanical cutting device, laser has now become an instrument of choice in many dental applications. Evidence suggests its use in initial periodontal therapy, surgery, and more recently, its utility in salvaging implant opens up a wide range of applications. More research with better designs are a necessity before lasers can become a part of dental armamentarium. This paper gives an insight to laser in periodontics. PMID:23066266

  15. Portable laser laboratory

    NASA Astrophysics Data System (ADS)

    Weir, J. T.

    1994-07-01

    A Portable Laser Laboratory (PLL) is being designed and built for the CALIOPE Program tests which will begin in October of 1994. The PLL is designed to give maximum flexibility for evolving laser experiments and can be readily moved by loading it onto a standard truck trailer. The internal configuration for the October experiments will support a two line DIAL system running in the mid-IR. Brief descriptions of the laser and detection systems are included.

  16. Thallium Mercury Laser Development

    DTIC Science & Technology

    1981-01-01

    THALLIUM MERCURY LASER DEVELOPMENT C. S. Liu and D. W. Feldman FINAL REPORT (PHASE III) (Period between Feb. 1, 1980 and Jan. 31, 1981) 0 Contract No...Pittsburgh, Pennsylvania 15235 Approved for public release;IDistribution Unlimited 1/i;THALLIUM MERCURY LASER DEVELOPMENT * , , IS C. S./Liu tRD. W /eldman...9 ’ t4 THALLIUM MERCURY LASER DEVELOPMENT C. S. Liu and D. W. Feldman Westinghouse R&D Center Pittsburgh, Pennsylvania 15235 1

  17. Excimer laser chemical problems

    SciTech Connect

    Tennant, R.; Peterson, N.

    1982-01-01

    Techniques need to be developed to maintain XeF and XeCl laser performance over long periods of time without degradation resulting from chemical processes occurring within the laser. The dominant chemical issues include optical damage, corrosions of laser materials, gas contamination, and control of halogen concentration. Each of these issues are discussed and summarized. The methods of minimizing or controlling the chemical processes involved are presented.

  18. Diode Pumped Fiber Laser

    DTIC Science & Technology

    1983-07-01

    acousto - optic beam deflector for greater absolute accuracy. The detection system was also upgraded to a response time of • 1 usec. The... 2 C. SUMMARY OF RESULTS.., 3 D . GENERAL PLAN 5 II. Nd:YAG FIBER PREPARATION 7 A. FIBER GROWTH 7 B. PHYSICAL PROPERTIES OF Nd:YAG...A. INTRODUCTION 25 B. GENERAL FORMALISM 26 C. FREE-SPACE LASERS 35 D . FIBER LASERS 43 1. Fiber Laser Configuration 43 2 . F

  19. Laser In Veterinary Medicine

    NASA Astrophysics Data System (ADS)

    Newman, Carlton; Jaggar, David H.

    1982-12-01

    Lasers have been used for some time now on animals for experimental purposes prior to their use in human medical and surgical fields. However the use of lasers in veterinary medicine and surgery per se is a recent development. We describe the application of high and low intensity laser technology in a general overview of the current uses, some limitations to its use and future needs for future inquiry and development.

  20. Polarization feedback laser stabilization

    DOEpatents

    Esherick, P.; Owyoung, A.

    1987-09-28

    A system for locking two Nd:YAG laser oscillators includes an optical path for feeding the output of one laser into the other with different polarizations. Elliptical polarization is incorporated into the optical path so that the change in polarization that occurs when the frequencies coincide may be detected to provide a feedback signal to control one laser relative to the other. 4 figs.

  1. Precision laser aiming system

    DOEpatents

    Ahrens, Brandon R.; Todd, Steven N.

    2009-04-28

    A precision laser aiming system comprises a disrupter tool, a reflector, and a laser fixture. The disrupter tool, the reflector and the laser fixture are configurable for iterative alignment and aiming toward an explosive device threat. The invention enables a disrupter to be quickly and accurately set up, aligned, and aimed in order to render safe or to disrupt a target from a standoff position.

  2. Etalon laser diode

    SciTech Connect

    Allen, L.B.; Koenig, H.G.; Rice, R.R.

    1981-08-18

    A laser diode is disclosed that is suitable for integrated and fiber optic applications requiring single transverse and single longitudinal mode operation. The single transverse mode is provided by making a gallium arsenide double heterostructural laser diode with a narrow stripe width and a relatively long length. The single longitudinal mode operation is provided by cracking the diode transverse to the stripe at one or more locations to form internal etalons in the laser cavity.

  3. Laser cutting plastic materials

    SciTech Connect

    Van Cleave, R.A.

    1980-08-01

    A 1000-watt CO/sub 2/ laser has been demonstrated as a reliable production machine tool for cutting of plastics, high strength reinforced composites, and other nonmetals. More than 40 different plastics have been laser cut, and the results are tabulated. Applications for laser cutting described include fiberglass-reinforced laminates, Kevlar/epoxy composites, fiberglass-reinforced phenolics, nylon/epoxy laminates, ceramics, and disposable tooling made from acrylic.

  4. Gigashot Optical Laser Demonstrator

    SciTech Connect

    Deri, R. J.

    2015-10-13

    The Gigashot Optical Laser Demonstrator (GOLD) project has demonstrated a novel optical amplifier for high energy pulsed lasers operating at high repetition rates. The amplifier stores enough pump energy to support >10 J of laser output, and employs conduction cooling for thermal management to avoid the need for expensive and bulky high-pressure helium subsystems. A prototype amplifier was fabricated, pumped with diode light at 885 nm, and characterized. Experimental results show that the amplifier provides sufficient small-signal gain and sufficiently low wavefront and birefringence impairments to prove useful in laser systems, at repetition rates up to 60 Hz.

  5. Laser Gyro Theory Extension.

    DTIC Science & Technology

    1980-12-01

    7 AA096 14S ARI ZONA UNIV TUCSON OPTICA SCIENCES CENTER F/6 20/5 LASER GYRO THE.ORY ESTENS ION(U)7 C So M 0 SCULLY IF33615-79-C-17N4 UNCLASSIIED...GYRO We have been working with scientists at Litton Industries in the development of a Zeeman laser gyro (ZLAG). We have developed a vector laser...Hutchings and V. Sanders are with Litton Industries , Woodland rate measurements with laser gyros (Section II). The remain- Hills, CA 91364. ing

  6. Shuttle Laser Altimeter

    NASA Technical Reports Server (NTRS)

    Bufton, Jack L.; Harding, David J.; Garvin, James B.

    1999-01-01

    The Shuttle Laser Altimeter (SLA) is a Hitchhiker experiment that has flown twice; first on STS-72 in January 1996 and then on STS-85 in August 1997. Both missions produced successful laser altimetry and surface lidar data products from approximately 80 hours per mission of SLA data operations. A total of four Shuttle missions are planned for the SLA series. This paper documents SLA mission results and explains SLA pathfinder accomplishments at the mid-point in this series of Hitchhiker missions. The overall objective of the SLA mission series is the transition of the Goddard Space Flight Center airborne laser altimeter and lidar technology to low Earth orbit as a pathfinder for NASA operational space-based laser remote sensing devices. Future laser altimeter sensors will utilize systems and approaches being tested with SLA, including the Multi-Beam Laser Altimeter (MBLA) and the Geoscience Laser Altimeter System (GLAS). MBLA is the land and vegetation laser sensor for the NASA Earth System Sciences Pathfinder Vegetation Canopy Lidar (VCL) Mission, and GLAS is the Earth Observing System facility instrument on the Ice, Cloud, and Land Elevation Satellite (ICESat). The Mars Orbiting Laser Altimeter, now well into a multi-year mapping mission at the red planet, is also directly benefiting from SLA data analysis methods, just as SLA benefited from MOLA spare parts and instrument technology experience [5] during SLA construction in the early 1990s.

  7. SYMMETRICAL LASER CRYSTALS.

    DTIC Science & Technology

    CRYSTAL GROWTH , SYMMETRY(CRYSTALLOGRAPHY), LASERS, SYNTHESIS, FERROELECTRIC CRYSTALS , FLUORESCENCE, IMPURITIES, BARIUM COMPOUNDS, ZIRCONATES...STRONTIUM COMPOUNDS, TITANATES, STANNATES, SAMARIUM, MANGANESE, REFRACTORY MATERIALS, OXIDES, SINGLE CRYSTALS .

  8. A quantum laser pointer.

    PubMed

    Treps, Nicolas; Grosse, Nicolai; Bowen, Warwick P; Fabre, Claude; Bachor, Hans-A; Lam, Ping Koy

    2003-08-15

    The measurement sensitivity of the pointing direction of a laser beam is ultimately limited by the quantum nature of light. To reduce this limit, we have experimentally produced a quantum laser pointer, a beam of light whose direction is measured with a precision greater than that possible for a usual laser beam. The laser pointer is generated by combining three different beams in three orthogonal transverse modes, two of them in a squeezed-vacuum state and one in an intense coherent field. The result provides a demonstration of multichannel spatial squeezing, along with its application to the improvement of beam positioning sensitivity and, more generally, to imaging.

  9. Laser Surface Treatment

    NASA Astrophysics Data System (ADS)

    Gnanamuthu, D. S.

    1980-10-01

    Experimental procedures and current state-of-the-art are presented for laser surface treating methods such as alloying, cladding, grain refining, and transformation hardening using a cw CO2 laser. Microstructural and x-ray analyses of the treated surfaces indicate that a laser beam can locally enhance surface properties. Laser alloying offers the possibility to selectively modify a low cost workpiece surface so that it has the desired high quality surface properties characteristic of high performance alloys. Laser cladding offers feasibility to apply high melting cladding alloys on low melting workpieces, to reduce the amount of dilution of cladding alloy with the workpieces, and the potential to apply dense ceramic claddings to metallic workpieces. Laser grain refining offers potential to either minimize or eliminate surface defects such as inclusions, intermetallic compounds, and pores, and to provide a refined grain structure. Laser transformation hardening provides the treated workpieces with a hard martensitic surface that has compressive stresses for enhanced fatigue life; in addition, reduction in wear rate of treated surfaces is achieved. This experimental study indicates that the use of lasers for surface treatment has several limitations. Further studies will provide better understanding for maximum utilization of laser surface treating processes.

  10. Dental lasers and science.

    PubMed

    Zakariasen, K L; Dederich, D N

    1991-07-01

    We have attempted to accomplish two purposes in this article. First, we have presented the case that extensive scientific investigation must form the base of our profession, that it must be an ongoing, continuous process and that laser dentistry must be developed through extensive scientific inquiry--as all of our treatment modalities should be. Second, we have presented many examples of the science involved in the development of laser dentistry. Lasers do have far-reaching potential for application to dentistry. We, as a profession, must insist that such laser development is done properly, not foisted upon us based on anecdotal reports and incomplete research.

  11. Deep space laser communications

    NASA Astrophysics Data System (ADS)

    Biswas, Abhijit; Kovalik, Joseph M.; Srinivasan, Meera; Shaw, Matthew; Piazzolla, Sabino; Wright, Malcolm W.; Farr, William H.

    2016-03-01

    A number of laser communication link demonstrations from near Earth distances extending out to lunar ranges have been remarkably successful, demonstrating the augmented channel capacity that is accessible with the use of lasers for communications. The next hurdle on the path to extending laser communication and its benefits throughout the solar system and beyond is to demonstrate deep-space laser communication links. In this paper, concepts and technology development being advanced at the Jet Propulsion Laboratory (JPL) in order to enable deep-space link demonstrations to ranges of approximately 3 AU in the next decade, will be discussed.

  12. Optofluidic random laser

    NASA Astrophysics Data System (ADS)

    Shivakiran Bhaktha, B. N.; Bachelard, Nicolas; Noblin, Xavier; Sebbah, Patrick

    2012-10-01

    Random lasing is reported in a dye-circulated structured polymeric microfluidic channel. The role of disorder, which results from limited accuracy of photolithographic process, is demonstrated by the variation of the emission spectrum with local-pump position and by the extreme sensitivity to a local perturbation of the structure. Thresholds comparable to those of conventional microfluidic lasers are achieved, without the hurdle of state-of-the-art cavity fabrication. Potential applications of optofluidic random lasers for on-chip sensors are discussed. Introduction of random lasers in the field of optofluidics is a promising alternative to on-chip laser integration with light and fluidic functionalities.

  13. Spaceborne laser radar.

    NASA Technical Reports Server (NTRS)

    Flom, T.

    1972-01-01

    Development of laser systems to acquire and track targets in applications such as the rendezvous and docking of two spacecraft. A scan technique is described whereby a narrow laser beam is simultaneously scanned with an equally narrow receiver field-of-view without the aid of mechanical gimbals. Equations are developed in order to examine the maximum acquisition and tracking rates, and the maximum target range for a scanning laser radar system. A recently built prototype of a small, lightweight, low-power-consuming scanning laser radar is described.

  14. Laser eye protection

    NASA Astrophysics Data System (ADS)

    Allen, Ralph G.; Labo, Jack A.; Mayo, Michael W.

    1990-07-01

    Laser applications have proliferated in recent years and as to be expected their presence is no longer confined to the laboratory or places where access to their radiation can be easily controlled. One obvious application where this is so is in military operations where various devices such as laser range finders target designators and secure communications equipment elevate the risk of exposure specifically eye exposure to unacceptable levels. Although the need for eye protection in the laboratory and other controlled areas has been appreciated since the invention of the laser the use of lasers in circumstances where safety or the risk of temporary loss of vision which can not always be ensured by administrative procedures has made adequate eye protection essential. It is the critical nature of many military operations that has driven the search for eye protection against both nuclear and laser radiation. At the same time the requirement to maintain useful vision during irradiation as well as advances in laser technology have complicated the problem enormously. Pertinent aspects of the problem such as laser characteristics- -pulse width repetition rate laser wavelength tunability or agility as well as laser power or energy have been placed in perspective. In addition possible effects on vision for various exposures have been estimated as have the characteristics required of eye protective devices. Various classes of devices are discussed and advantages and disadvantages noted. 1.

  15. Trends in laser micromachining

    NASA Astrophysics Data System (ADS)

    Gaebler, Frank; van Nunen, Joris; Held, Andrew

    2016-03-01

    Laser Micromachining is well established in industry. Depending on the application lasers with pulse length from μseconds to femtoseconds and wavelengths from 1064nm and its harmonics up to 5μm or 10.6μm are used. Ultrafast laser machining using pulses with pico or femtosecond duration pulses is gaining traction, as it offers very precise processing of materials with low thermal impact. Large-scale industrial ultrafast laser applications show that the market can be divided into various sub segments. One set of applications demand low power around 10W, compact footprint and are extremely sensitive to the laser price whilst still demanding 10ps or shorter laser pulses. A second set of applications are very power hungry and only become economically feasible for large scale deployments at power levels in the 100+W class. There is also a growing demand for applications requiring fs-laser pulses. In our presentation we would like to describe these sub segments by using selected applications from the automotive and electronics industry e.g. drilling of gas/diesel injection nozzles, dicing of LED substrates. We close the presentation with an outlook to micromachining applications e.g. glass cutting and foil processing with unique new CO lasers emitting 5μm laser wavelength.

  16. Fusion reactor pumped laser

    DOEpatents

    Jassby, Daniel L.

    1988-01-01

    A nuclear pumped laser capable of producing long pulses of very high power laser radiation is provided. A toroidal fusion reactor provides energetic neutrons which are slowed down by a moderator. The moderated neutrons are converted to energetic particles capable of pumping a lasing medium. The lasing medium is housed in an annular cell surrounding the reactor. The cell includes an annular reflecting mirror at the bottom and an annular output window at the top. A neutron reflector is disposed around the cell to reflect escaping neutrons back into the cell. The laser radiation from the annular window is focused onto a beam compactor which generates a single coherent output laser beam.

  17. Lasers and avionic integration

    NASA Astrophysics Data System (ADS)

    Willams, J. S.

    1983-07-01

    Interrogative applications of laser technology are considered, taking into account the extent to which a centralized source of information can be used to service a number of functions which need to be performed in an airframe, and, in addition, also the potential of the laser as probing device. Aspects of laser technology and air vehicle communications are discussed along with laser based techniques for processing and storage of information. Attention is given to data transmission within the aircraft, communications external to the air vehicle, Fourier optics, holographic methods, real-time processing, Bragg cells and spectrum analysis, optical bistable devices, and optical data storage.

  18. Laser applications in phlebology

    NASA Astrophysics Data System (ADS)

    Longo, Leonardo; Mancini, S.; Postiglione, Marco; Postiglione, M. G.

    2001-06-01

    PURPOSE: review of laser used in phlebology METHOD: critical analysis of scientific data taken from the literature and based on 25 years personal experience. RESULTS: we have three groups of laser applications in phlebology: for the diagnosis, as physical therapy and as surgical therapy. DISCUSSION AND CONCLUSION: the laser-doppler studies the microcirculations, the no-surgical therapy shown positive results in the treatment of venous ulcers and for the wound healing. It could be indicate also as antiphlogistic and anti-edema therapy, in superficial thrombophlebitis. The surgical laser is useful for the surgical cleaning of ulcers, for haemorroids, angiomas and telangiectases.

  19. Lighting with laser diodes

    NASA Astrophysics Data System (ADS)

    Basu, Chandrajit; Meinhardt-Wollweber, Merve; Roth, Bernhard

    2013-08-01

    Contemporary white light-emitting diodes (LEDs) are much more efficient than compact fluorescent lamps and hence are rapidly capturing the market for general illumination. LEDs are also replacing halogen lamps or even newer xenon based lamps in automotive headlamps. Because laser diodes are inherently much brighter and often more efficient than corresponding LEDs, there is great research interest in developing laser diode based illumination systems. Operating at higher current densities and with smaller form factors, laser diodes may outperform LEDs in the future. This article reviews the possibilities and challenges in the integration of visible laser diodes in future illumination systems.

  20. Laser processing with specially designed laser beam

    NASA Astrophysics Data System (ADS)

    Asratyan, A. A.; Bulychev, N. A.; Feofanov, I. N.; Kazaryan, M. A.; Krasovskii, V. I.; Lyabin, N. A.; Pogosyan, L. A.; Sachkov, V. I.; Zakharyan, R. A.

    2016-04-01

    The possibility of using laser systems to form beams with special spatial configurations has been studied. The laser systems applied had a self-conjugate cavity based on the elements of copper vapor lasers (LT-5Cu, LT-10Cu, LT-30Cu) with an average power of 5, 10, or 30 W. The active elements were pumped by current pulses of duration 80-100 ns. The duration of laser generation pulses was up to 25 ns. The generator unit included an unstable cavity, where one reflector was a special mirror with a reflecting coating. Various original optical schemes used were capable of exploring spatial configurations and energy characteristics of output laser beams in their interaction with micro- and nanoparticles fabricated from various materials. In these experiments, the beam dimensions of the obtained zones varied from 0.3 to 5 µm, which is comparable with the minimum permissible dimensions determined by the optical elements applied. This method is useful in transforming a large amount of information at the laser pulse repetition rate of 10-30 kHz. It was possible to realize the high-precision micromachining and microfabrication of microscale details by direct writing, cutting and drilling (with the cutting width and through-hole diameters ranging from 3 to 100 µm) and produce microscale, deep, intricate and narrow grooves on substrate surfaces of metals and nonmetal materials. This system is used for producing high-quality microscale details without moving the object under treatment. It can also be used for microcutting and microdrilling in a variety of metals such as molybdenum, copper and stainless steel, with a thickness of up to 300 µm, and in nonmetals such as silicon, sapphire and diamond with a thickness ranging from 10 µm to 1 mm with different thermal parameters and specially designed laser beam.