Excimer Laser Technique Research Articles

A New Elliptical Excision for Corneal Transplantation Using an Excimer Laser

To the Editor. —Current standard corneal transplantation techniques use circular, round, mechanical trephines either operated by hand or motor driven, under visual control through the operating microscope. The anatomic and functional results of this sight-improving procedure are acceptable. 1 The two major problems of the procedure are disturbing astigmatism and immunologic graft rejections. Excessive corneal astigmatism and optical irregularities are caused by incongruent cut surfaces of donor and patient corneas and disparities in corneal thickness. 1 Immunologic graft rejection occurs in 10% of avascular corneas and increases in frequency in vascularized corneas and as the diameter of the corneal graft increases. While for optical purposes it is desirable to have the corneal graft as large as possible, immunologic requirements aim for the opposite result. The ultraviolet excimer laser technique enables us to overcome the mechanical limitations of the trephination procedure and to produce noncircular trephinations. 2,3 We now introduce a

Free-radical polymerization at high pressure studied by excimer laser techniques

Abstract The application of novel excimer laser techniques to the detailed study of free-radical homo- and copolymerizations is outlined. The method allows to measure rate coefficients of propagation and termination as a function of pressure, temperature, conversion, and free-radical chain-length.

Excimer Laser Instrumentation and Technique for Human Corneal Surgery

The design and development of the instrumentation utilized during the clinical and histopathologic evaluations of the first human eyes treated by argon fluoride excimer laser radiation are described. The laser, optical, alignment, measurement, and control subsystems required for this research were constructed to create a laser beam that has an axially symmetric energy distribution, can be calibrated and measured, can be aligned with the target tissue, and can be manipulated to excise surface tissue. The use of this excimer laser system has demonstrated that a nonuniform superficial lamellar keratectomy can be produced to excise areas of opacified, scarred, or abnormal cornea or to create a new anterior corneal curvature in attempts to correct refractive errors.

Excimer laser direct etching of GaAs

The direct etching of GaAs substrates by excimer laser light has been studied at wavelengths of 193 nm (ArF). 248 nm (KrF) and 351 nm (XeF). For absorbed laser fluences greater than the direct etching fluence thresholds of 23 mJ cm-2 for ArF, 33 mJ cm-2 for KrF and 80 mJ cm-2 for XeF, the authors observe direct etching in air to depths of order one nanometre per pulse. For low-fluence exposures in either vacuum (10-2 Torr) or N2 (1 atm) environments the etch depth per pulse is less than a quarter of that observed when exposure takes place in air. For higher fluence exposures ( approximately 250 mJ cm-2) the etched regions show signs of melting. Using a line-narrowed KrF excimer laser and holographic interference techniques gratings of period 1.5 mu m were directly etched in GaAs substrates.

Ultrafast deep UV Lithography with excimer lasers

The use of high-power pulsed excimer lasers for photolithography is described for the first time. Short exposure times, high resolution and absence of speckle are experimentally demonstrated. Using a XeCl laser at 308 nm and a KrF laser at 248 nm, excellent quality images are obtained by contact printing in two positive photoresists. Resolution down to 1000 line-pairs/mm is demonstrated. These images are comparable to state-of-the-art lithography done with conventional lamps; the major difference is that the excimer laser technique is ∼ 2 orders of magnitude faster. Preliminary results on reciprocity behavior in several resists are also presented.

Ultrafast High-Resolution Contact Lithography with Excimer Lasers

A new technique for speckle-free, fine-line high-speed lithography using high-power pulsed excimer lasers is described and demonstrated. Use of stimulated Raman shifting is proposed for obtaining the most desirable set of spectral lines for any resist. This permits, for the first time, the optimization of the exposur wavelengths for a given resist, rather than the reverse situation. Excellent-quality images are obtained in 1-µm-thick diazo-type photoresists such as ® AZ-2400 and a diazonaph-thoquinone-®Novolak resist system by means of contact printing with a XeCl laser at 308 nm and a KrF laser at 248 nm. Resolution down to 1000 line pairs per millimeter is experimentally demonstrated. These images are comparable to state-of-the-art contact lithography obtained with conventional lamps. The major difference is that the excimer laser technique is approximately two orders of magnitude faster. Tests on reciprocity failure ins everal resists indicate a decrease in sensitivity by only a factor of three, despite the ≅108 times larger power density used in the laser exposures. The possibility of photochemical reactions being diflerent from those taking place in the case of lamp exposures is discussed in view of these results.