Nonlinear Optical Crystals: A Complete Survey

• We produced corneal excisions with nanosecond (ns)-, picosecond-, and femtosecond (fs)-pulsed lasers at visible wavelengths. The threshold energy for ablation was proportional to the square root of the pulse duration and varied from 2.5 microjoules (μJ) at 100 fs to 500 μJ at 8 ns. Excisions made with picosecond and femtosecond lasers were ultrastructurally superior to those made with nanosecond lasers and, at pulse energies near threshold, showed almost as little tissue damage as excisions made with excimer lasers at 193 nm. We conclude that ultra-short-pulsed lasers at visible and near-infrared wavelengths are a possible alternative to excimer lasers for corneal surgery and might have advantages over conventional ophthalmic neodymium-YAG lasers for some intraocular applications.

https://jamanetwork.com/journals/OPHTH/articlepdf/637776/archopht_107_4_038.pdf

Corneal Ablation by Nanosecond, Picosecond, and Femtosecond Lasers at 532 and 625 nm

The results of recent work directed towards the application of excimer lasers to angioplasty are presented. Several laser-tissue interactions are examined, including the effect of the XeCl laser optical pulse duration (7-300 ns) on the threshold fluence for ablation of arterial wall and on the quality of the cut in human postmortem artery, the potential for altering the ablation threshold fluence of arterial plaque in swine by treatment with hematoporphyrin derivative, and the healing response of swine arterial wall to surgical irradiation with an argon laser and a pulsed XeCl laser. The dependence of damage thresholds and transmission properties of selected commercial fused silica fibers on the laser pulsewidth and wavelength are determined.

Excimer laser angioplasty: Tissue ablation, arterial response, and fiber optic delivery

Damage measurements of fused silica fibres using long optical pulse XeCl lasers

The transmission of uncoated and antireflection (AR)-coated CaF2 windows has been measured during long KrF laser exposures. Samples were tested for up to 75 million pulses in front of an industrial-grade KrF excimer laser at high repetition rates (200–300 Hz) and moderately high energy fluence (220–550 mJ/cm2). In this fluence range bare CaF2 performs much better than the best fused silicas currently available. Various AR coatings (whose structures were initially unknown to us) were deposited on CaF2 substrates polished to two distinct surface finishes. We determined the coating structures by using x-ray spectroscopy to identify positively all elements that were heavier than fluorine and fluorescence Rutherford backscattering spectroscopy to determine the layer structure and approximate layer thicknesses. We confirmed the structures by comparing measured UV transmission spectra with computer simulations. This study reveals excellent performance for SiO2/Al2O3/SiO2/Al2O3 coatings on highly polished substrates, which provided two-sided transmission in excess of 99.8% at 248 nm and no measurable deterioration after 75 million pulses. A MgF2/Al2O3 coating also performed quite well, while a hafnia-containing coating (MgF2/HfO2/LaF3) exhibited anomalous behavior. All-fluoride coatings consisting of MgF2/LaF3/MgF2 and MgF2/LaF3/AlF3 had good durability but lower starting transmission as a result of scatter losses in the LaF3 layer. These results demonstrate the availability of AR-coated CaF2 optics for high-power KrF laser applications with high transmission and no sign of degradation up to ~ 7 × 107 pulses.

Testing of the durability of single-crystal calcium fluoride with and without antireflection coatings for use with high-power KrF excimer lasers.

We used 20 ns, 248 nm pulses to study surface and bulk damage in bare, polished samples of UV-transmitting glasses, fluoride crystals, and isomorphs of potassium dihydrogen phosphate (KDP). The intent was to test enough samples to establish the safe operating limits for currently available windows and crystals finished by routine techniques for optical fabrication. In fluoride crystals, thresholds for bulk inclusion damage and for rear-surface damage were comparable. The median rear-surface threshold was 16 J/cm2. The fluence limit in fused silica windows was determined by the threshold for rear-surface damage, which ranged from 5 to 9 J/cm2. For the isomorphs of KDP, the limiting fluence was the threshold for front-surface damage, which ranged from 3 to 9 J/cm2.

Bulk And Surface Damage Thresholds Of Crystals And Glasses At 248 nm

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Bulk And Surface Damage Thresholds Of Crystals And Glasses At 248 nm