Eximer Laser Research Articles

Optimized refractive surgery in keratoconus

Purpose: The aim of the study is to compare the refractive results after simultaneous TransPRK and Cross-linking procedure for treatment of keratoconus with optimized and non-optimized customized ablation profiles; to introduce the concept of optimization in keratoconus and discuss its clinical significance; to find predictive factors for better refractive outcomes in simultaneous combined procedures and to propose therapeutic algorithm. Methods: Syrius schimpflug aberrometer (Schwind) was used to create non-optimized custom and optimized custom ablation profiles in keratoconic corneas. TransPRK ablation was performed with Schwind Amaris Eximer Laser (500 Hz). Cross-linking was done with Avedro cross-linking suit. Analysis of preoperative and postoperative refraction, visual acuity, keratometric and aberometric data was done for both groups. Correlative analysis of the preoperative and postoperative variables was done with Pierson statistical analysis. Results: 44 patients (70 eyes), age 19-67, 29 eyes with optimization, 41 eyes without optimization were followed for 18 months. A positive correlation was found between CCT and the amount of postoperative flattening in patients over 40 years of age. No correlation was found with Kavg. Conclusions: Long term results after simultaneous TransPRK + Cross linking show stability and safety. Optimization of refraction brings better refractive results compared to non-optimized procedure. It can be safely performed in thinner corneas and compensates for the hypermetropic shift generated by the cross-linking procedure.

300-mW narrow-linewidth deep-ultraviolet light generation at 193 nm by frequency mixing between Yb-hybrid and Er-fiber lasers

A narrow-linewidth, high average power deep-ultraviolet (DUV) coherent laser emitting at 193 nm is demonstrated by frequency mixing a Yb-hybrid laser with an Er-fiber laser. The Yb-hybrid laser consists of Yb-fiber lasers and an Yb:YAG amplifier. The average output power of the 193 nm laser is 310 mW at 6 kHz, which corresponds to a pulse energy of 51 μJ. To the best of our knowledge, this is the highest average power and pulse energy ever reported for a narrow-linewidth 193 nm light generated by a combination of solid-state and fiber lasers with frequency mixing. We believe this laser will be beneficial for the application of interference lithography by seeding an injection-locking ArF eximer laser.

New Micromachining Technique for Unworkable Sapphire by Highly Coalesced Ion Implantation and Eximer Laser Irradiation

New Micromachining Technique for Unworkable Sapphire by Highly Coalesced Ion Implantation and Eximer Laser Irradiation

A Line Pair Indicator Made of Gd Film for Evaluating Spatial Resolution

A device for evaluating the spatial resolution of a neutron imaging system was developed. Using laser processes, line- pair patterns were fabricated on a 0.005-mm-thick Gd film evaporated on a glass plate. Large line pairs of widths ranging from 0.2 to 2 mm were machined using an Nd:YVO 4 laser (0.03 mm spot size) and displayed on a brightness field, while small line pairs of widths ranging from 0.01 to 0.1 mm were created using an eximer laser on a dark field. A scanning electron microscope (SEM) observation determined that, although the large line pairs machined using the Nd:YVO 4 laser were chipped on the corners of the Gd bars, the difference between the measured and designed line- pair widths was controlled absolutely within 0.02 mm. In the small line pairs of less than 0.1 mm width processed using the eximer laser, edges sharper than those of the large line pairs were formed. In neutron imaging tests using a LiF/ZnS(Ag) scintillator and a CCD camera system, good contrast images were obtained with the brightness field, even at 0.005 mm thickness. The small line pairs on the dark field were observed using a LiF single crystal detector having an ultra-high spatial resolution of approximately 0.005 mm. Splits in the small line pairs of as little as 0.01 mm wide were shown with good contrast on the images.

E-2-2 エピタキシャルPZT薄膜を用いた高効率圧電型振動発電素子に関する研究(マイクロナノメカトロニクス(2),口頭発表)

We fabricated piezoelectric energy harvesters composed of c-axis oriented Pb(Zr,Ti)O_3 (PZT) thin films transferred onto stainless steel substrates.In order to improve resonance frequency,we designed a cantilever with a tip mass.PZT thin firms were epitaxially grown on MgO substrates using rf-magnetoron sputtering and transferred onto stainless steel substrate by eximer laser liftoff.Transferred PZT thin firms had a low dielectric constant (ε_r=340) and high piezoelectric coefficient(e_<31.1>=-4.76 C/m^2).The energy harvester had a resonance frequency of 143.2 Hz.At the optimal load resistance of 90 kΩ and resonance frequency of 143.2 Hz, theenergy harvester generated output power of 2.02μW at an acceleration of 1m/s^2 and 49μW at acceleration of 7.5 m/s^2.

Cancer cells uptake porphyrinsviaheme carrier protein 1

Although exogenous porphyrin accumulation in cancer cells is important for the success of photodynamic therapies, the mechanism is not clear. We hypothesized that a newly reported transporter, heme carrier protein 1 (HCP1), is highly expressed in cancer cells, and transports porphyrins into the cells. We investigated the following three unknowns: whether cancer cells take up hematoporphyrin derivative via HCP1, whether HCP1 is involved in photodynamic therapies, and whether cancer cells highly express HCP1. First, when HCP1-overexpressed cells were treated with hematoporphyrin derivative and then exposed to an eximer laser beam, they emitted a significantly higher intensity of hematoporphyrin derivative fluorescence and became more susceptible to the laser beam than control. Second, when three other types of cancer cells with silenced HCP1 were treated with hematoporphyrin derivative and then exposed to the laser beam, they emitted a significantly lower intensity of hematoporphyrin derivative fluorescence. Third, non-cancer cells slightly expressed HCP1; on the other hand, the three other types of cancer cells clearly expressed HCP1. These results indicated that cancer cells uptake hematoporphyrin derivative via HCP1 and over-expression of HCP1 increases the efficacy of photodynamic therapies by increasing porphyrin accumulation in the cells. This is the first report about a transporter of porphyrin in cancer cells.

Synthesis and Characterization of a Pt/NiO/Pt Heterostructure for Resistance Random Access Memory

We examined the electrical properties and microstructure of NiO produced using a sol-gel method and Ni nitrate hexahydrate (<TEX>$Ni[NO_3]_2{\cdot}6H_2O$</TEX>) to investigate if this NiO thin film can be used as an insulator layer for resistance random access memory (ReRAM) devices. It was found that as-prepared NiO film was polycrystalline and presented as the nonstoichiometric compound <TEX>$Ni_{1+x}O$</TEX> with Ni interstitials (oxygen vacancies). Resistances-witching behavior was observed in the range of 0~2 V, and the low-resistance state and high-resistance state were clearly distinguishable (<TEX>${\sim}10^3$</TEX> orders). It was also demonstrated that NiO could be patterned directly by KrF eximer laser irradiation using a shadow mask. NiO thin film fabricated by the sol-gel method does not require any photoresist or vacuum processes, and therefore has potential for application as an insulating layer in low-cost ReRAM devices.

Application of umbilical cord serum eyedrops after laser epithelial keratomileusis

To investigate the efficacy of umbilical cord serum eyedrops after laser epithelial keratomileusis (LASEK). Sixty patients (120 eyes) with myopia who underwent LASEK were studied. Thirty-two patients (64 eyes) were treated with 20% umbilical cord serum eyedrops in combination with conventional treatment (group A), and 28 patients (56 eyes) received conventional treatment only (group B). Epithelial healing time was analysed. Visual acuity, refraction, haze score (0-4) and tear film and ocular surface parameters were evaluated at 1, 2, 4 and 12 weeks after LASEK. The concentration of transforming growth factor (TGF)-β1 in tears was measured with ELISA at 1 week after LASEK. No significant differences in visual acuity and refraction were found between groups. The mean time to epithelial healing was 3.53 ± 1.19 days in group A and 3.91 ± 1.41 days in group B (p = 0.18). The mean haze scores at 2 and 4 weeks were 0.59 ± 0.80 and 0.31 ± 0.54 in group A and 1.06 ± 0.91 (p = 0.02) and 0.69 ± 0.78 (p = 0.03) in group B. Four and 12 weeks after LASEK, tear film break-up time was longer and keratoepitheliopathy score was lower in group A compared with group B. The mean concentration of TGF-β1 was lower in group A compared with group B (p = 0.01). Application of 20% umbilical cord serum eyedrops in addition to conventional treatment after LASEK can reduce early postoperative corneal haze and improve tear film and ocular surface parameters.

Simultaneous treatment of the broken corneal flap during ultra-thin flap LASIK

Objective To observe the effect of primary operation of corneal flap breakage in ultra-thin flap LASIK. Methods 7 eyes of 7 patients who confronted corneal flap breakage during ultra-thin flap LASIK in our department during Feb. 2006-Oct. 2009 received primary treatment during the operation： erase the broken flap epithelium of the uncutted part within the laser treatment area ,while expose the corneal stroma bed of the eutted part and deliver the laser treatment. Results All the 7 patients accepted the operation smoothly ,There were no epithelium implant ,flap displacement or other complications. The vision kept stable 1-3 months after the opera- tion , no correct vision decrease. Haze happened in 3 eyes 3 months after the operation, all of them are 0.5 grade. Conclusion primary operation of corneal flap breakage in ultra-thin flap LASIK is safe and effective. Key words: Eximer laser in-situ keratomileusis; ultra-thin coneal flap; Complication; Myopia corretion

Role of Topical Ascorbic Acid in Management of Refractory Corneal Ulcer

Ascorbic acid, a water soluble vitamin, helps in collagen assembly, synthesis of neurotransmitters, has immune functions and also acts as a major antioxidant in the body. Refractory corneal ulcer is a challenging situation faced by every ophthalmologist in developing countries. Available treatment options for refractory corneal ulcer are bandage contact lens, grid keratotomy, therapeutic penetrating keratoplasty, amniotic membrane transplantation, nerve growth factors, aprotinin [proteases inhibitor]. These treatment options are costly and require expertise in preparation and use. Topical ascorbic acid has been known to have good results in caustic injury of cornea and in free radical damage after eximer laser surgery. This makes it a potential cost-effective candidate to be studied as an alternative in addition to conservative treatment for treating refractory corneal ulcer. This study aims to study the role of topical ascorbic acid in treatment of refractory corneal ulcers.

단주기 광섬유 격자(Fiber Grating)와 장주기 광섬유 격자의 온도 의존성 비교

An optical fiber short period grating of 0.7 nm as a 3 dB wavelength linewidth was fabricated using a Gaussian distributed KrF Eximer laser and a phase mask. This grating has temperature dependancy of 0.01 nm/ over the range of -10 ~ 70 and no difference between temperature directions. An optical fiber long period grating of 14.22 nm as a 3 dB linewidth was also fabricated using a amplitude mask and has dependancy of 0.01 nm/ over the same range.

Capacitorless 1T-DRAM on Crystallized Poly-Si TFT

The single-transistor dynamic random-access memory (1T-DRAM) using a polycrystalline-silicon thin-film transistor (poly-Si TFT) was investigated. A 100-nm amorphous silicon thin film was deposited onto a 200-nm oxidized silicon wafer via low-pressure chemical vapor deposition (LPCVD), and the amorphous silicon layer was crystallized via eximer laser annealing (ELA) with a KrF source of 248 nm wavelength and 400 mJ/cm2 power. The fabricated capacitor less 1T-DRAM on the poly-Si TFT was evaluated via impact ionization and gate-induced drain leakage (GIDL) current programming. The device showed a clear memory margin between the "1" and "0" states, and as the channel length decreased, a floating body effect which induces a kink effect increases with high mobility. Furthermore, the GIDL current programming showed improved memory properties compared to the impact ionization method. Although the sensing margins and retention times in both program methods are commercially insufficient, it was confirmed the feasibility of the application of 1T-DRAM operation to TFTs.

59.3: Bridged‐grain (BG) Eximer Laser Annealing (ELA) Polycrystalline Silicon Thin Film Transistors (TFTs)

AbstractA new technique bridged‐grain (BG) was introduced. Using this BG eximer laser annealing (ELA) poly‐Si as an active layer, the grain boundary effects can be reduced. Important electrical properties such as sub‐threshold swing, threshold voltage, maximum field effect mobility, leakage current, on‐off ratio and device uniformity across the substrate can all be improved using the present technique. The improvement can be achieved at low cost, thus making inexpensive, high performance LTPS TFT a reality.

Development of EKC after Eximer Laser Photorefractive Surgery and Subsequent Recurrence of EKC-like Keratitis

This research focuses on four cases of patients having undergone eximer laser photorefractive surgery who were diagnosed with adenoviral keratoconjunctivitis during the postoperative period and who later developed epidemic keratoconjunctivitis (EKC)-like keratitis. Two of the patients had undergone laser-assisted subepithelial keratectomy (LASEK), one had undergone laser in situ keratomileusis and one had photorefractive keratectomy. After the surgery adenoviral keratoconjunctivitis and recurrent late-developing EKC-like keratitis were observed in the patients. Recurrent late-developing EKC-like keratitis occurred in one of the patients, who had received LASEK as many as three times. The others had only one or two episodes.The corneal infiltrates of keratitis mainly occurred in the central cornea. Successful resolution of recurrent late-developing EKC-like keratitis was achieved through the use of topical steroids without sequelae and the final best-corrected visual acuity was as good as the base line. These keratitis infiltrates have been presumed to represent an immune response to the suspected adenoviral antigens deposited in corneal stroma during the primary adenoviral infection. Previous reports argued that patients with a history of adenoviral ketatoconjunctivitis were succeptible to adenoviral keratoconjunctivitis becoming reactivated; however, in our research, our patients had their first adenoviral infections after the eximer laser photorefractive surgery and reactivation was confirmed. We recommend that attention be paid to adenoviral infection after laser refractive operations, because these patients seem to have more frequent recurrences.

광섬유 브래그 격자(Fiber Bragg grating) 제작과 제작 조건에 따른 특성 향상

Optical fiber Bragg grating to have the lowest transmitivity at 1549.9nm wavelength was fabricated using a Gaussian distributed KrF Eximer laser of 248nm lasing wavelength and a phase mask of 1.072um period. The proper alignment of an optic setup to fabricate fiber gratings was investigated and the reproductivity of the grating fabrication was examined using the obtained optimum fabrication condition in this experiment.

LASER TRANSFER PROCESSING AND THE INTEGRATION OF FERROELECTRIC FILMS

ABSTRACT Thin films of barium strontium titanate (BST), lanthanum modified bismuth titanate (LBT) and lead zirconate titanate (PZT) were fabricated by sol-gel methods onto sapphire substrates. They were transferred to a second substrate by using UV eximer laser radiation to delaminate the films from the fabrication substrate. Scanning electron microscopy revealed melting at the interfacial region of the LBT and PZT films, thus providing the delamination mechanism, but melting was not observed in the BST films. Only the PZT film, after laser transfer, retained its ferroelectric properties, with remnant polarisation of ∼30 μC/cm2, and a high coercive field of 150 kV/cm.

Diamond-like phase formation in an amorphous carbon films prepared by periodic pulsed laser deposition and laser irradiation method

Diamond-like carbon (DLC) films were fabricated by pulsed laser ablation of a liquid target. During deposition process the growing films were exited by a laser beam irradiation. The films were deposited onto the fused silica using 248 nm KrF eximer laser at room temperature and 10 −3 mbar pressure. Film irradiation was carried out by the same KrF laser operating periodically between the deposition and excitation regimes. Deposited DLC films were characterized by Raman scattering spectroscopy. The results obtained suggested that laser irradiation intensity has noticeable influence on the structure and hybridization of carbon atoms deposited. For materials deposited at moderate irradiation intensities a very high and sharp peak appeared at 1332 cm −1, characteristic of diamond crystals. At higher irradiation intensities the graphitization of the amorphous films was observed. Thus, at optimal energy density the individual sp 3-hybridized carbon phase was deposited inside the amorphous carbon structure. Surface morphology for DLC has been analyzed using atomic force microscopy (AFM) indicating that more regular diamond cluster formation at optimal additional laser illumination conditions (∼20 mJ per impulse) is possible.

Stephen Edward Smith

Stephen Edward Smith

Preparation of CuCr2Se4/ZnSe layered films on glass substrates by laser ablation

Films of chalcogenide spinel CuCr2Se4 were prepared by laser ablation. Targets were synthesized by melting in silica tubes and connected to a rotating drum. The targets were then evaporated by a XeCl eximer laser (wavelength, 308 nm; pulse duration, 20 ns; pulse power, 10 mJ). The target and the substrate during deposition were rotated at a rate of 150 rpm in a vacuum chamber. The deposition of CuCr2Se4/ZnSe multilayer films was studied, their thickness was controlled, and their morphology was examined by scanning electron microscopy. The crystal structure and magnetic properties of monolayer and multilayer films were investigated.

Long-Term Results of Presbyopic Corneal Surface Ablation with Eximer Laser

Purpose: To evaluate the efficacy, safety, and subjective symptoms of patients who underwent presbyopic corneal surface ablation. Methods: Excimer laser surgery with MEL80 for refractive errors and presbyopia was performed on 128 eyes of 67 patients. Uncorrected and best-corrected visual acuity, distance-corrected near-visual acuity, spectacle near-addition for Jaeger 1, depth of focus, spherical aberration, and subjective symptoms were evaluated before surgery and 1 year after surgery. Results: This study consisted of a myopia group (56 eyes), an emmetropia group (spherical equivalent ≤ ±0.75D, 19 eyes), and a hyperopia group (53 eyes). Presbyopic corneal ablation improved distance and near uncorrected visual acuity, and distance-corrected near visual acuity at postoperative 12 months. There was no significant change in best-corrected visual acuity but there was a significant decrease in the emmetropia only group. Useful near visual acuity (≥20/40) was found in 96 eyes (75%) and spectacle near addition for Jaeger 1 decreased. Our results showed a significant increase of spherical aberration (from -0.19 µm to 0.11 µm) and depth of focus (from 1.45D to 1.69D). A significant positive correlation was found between spherical aberration and uncorrected far and near visual acuity and depth of focus. Loss of two lines of best corrected visual acuity occurred in 11 eyes (8.5%) at far vision and in 7 eyes (5.5%) at near vision. In general, patient satisfaction was good. Conclusions: Presbyopic corneal ablation with MEL80 showed good distant and near visual results and a wide depth of focus induced by increased spherical aberration.